Short answer: Your friends who think torture is effective at getting reliable information are wrong.
Army Field Manual 34-52 Chapter 1 says:
“Experience indicates that the use of force is not necessary to gain the cooperation of sources for interrogation. Therefore, the use of force is a poor technique, as it yields unreliable results, may damage subsequent collection efforts, and can induce the source to say whatever he thinks the interrogator wants to hear.”
The C.I.A.’s 1963 interrogation manual stated:
Intense pain is quite likely to produce false confessions, concocted as a means of escaping from distress. A time-consuming delay results, while investigation is conducted and the admissions are proven untrue. During this respite the interrogatee can pull himself together. He may even use the time to think up new, more complex ‘admissions’ that take still longer to disprove.
The act of torturing can even interfere with a subject's ability to tell the truth.
Solid scientific evidence on how repeated and extreme stress and pain affect memory and executive functions (such as planning or forming intentions) suggests these techniques are unlikely to do anything other than the opposite of that intended by coercive or 'enhanced' interrogation.
This Newsweek article also links to the Trinity College Institute of Neuroscience in Dublin that has a paper in the journal Trends in Cognitive Science. It will cost you nearly $40 for the paper itself though.
In specifically dealing with the post 9/11 world, a work entitled A utilitarian argument against torture interrogation of terrorists states in its abstract:
Drawing from criminology, organizational theory, social psychology, the historical record, and my interviews with military professionals, I assess the potential of an official U.S. program of torture interrogation from a practical perspective. The central element of program design is a sound causal model relating input to output. I explore three principal models of how torture interrogation leads to truth: the animal instinct model, the cognitive failure model, and the data processing model. These models show why torture interrogation fails overall as a counterterrorist tactic.
Anyone remember the Star Trek episode that dealt with this issue? And this was before Waterboarding was part of our lexicon.
Furthermore, the Society for the Psychological Study of Social Issues states:
there is no evidence that torture is an effective means of gathering reliable information. Many survivors of torture report they that would have said anything to “make the torture stop” (Mayer, 2005; McCoy, 2005). Those who make the claim that “torture works” offer as evidence only unverifiable anecdotal accounts.
LiveScience sums it up very well in the title of an article from October 2007:
Torture Has a Long History ... of Not Working
I went through the USAF SERE School, and I can tell you that even though we weren't "tortured" we were placed under numerous stressors, and we would do as many deceitful things to get out of those situations as possible (i.e. tell them what they wanted as opposed to the truth). And we were even taught how to evade the torture by supplying plausible lies, and then "recover" from anything that may have been detrimental to our position as a POW.
EDIT TO ADD: Someone asked if there are any methods for getting information quickly, and reliably. The answer is, "It depends." There are many, many techniques out there (Good Cop-Bad Cop, Surprise, sympathy, etc.). All of those really depend on the state of mind of the subject. One really needs to get to know the subject before you can start to whittle away at them and find what you want/need. And even then, it is wildly variable and depends a great deal on psychology. The link to the Army Field Manual 34-52 mentions some specialized training required:
The interrogator requires specialized training in international regulations, security, and neurolinguistics.
Neurolinguistics is a behavioral communications model and a set of procedures that improve communication skills. The interrogator should read and react to nonverbal communications. An interrogator can best adapt himself to the source's personality and control his own reactions when he has an understanding of basic psychological factors, traits, attitudes, drives, motivations, and inhibitions.
Also, keep in mind that HUMINT can be gathered much more reliably via other methods than direct interrogation. The recent example of the courier that led to the raid on Osama bin Laden was all HUMINT gathered via tailing and observation. DuckMaestro is interested in data, and every source I find says that interrogation isn't even a science, but rather an art... How is one supposed to get data on that? A scholarly paper on Police Interrogation techniques, even highlights the art nature more than anything (PDF File). The most effective that has some backing by studies seems to be the Reid Technique of investigative interviewing, which seems to be a recap from the Army Field Manual.
WHY USE IT? So why do people use it, or promote it? While probably beyond the scope of the answer, I wanted to address this with a couple of thoughts. First of all, human beings are animals. There is a visceral need to hurt your enemy. If you have captured an enemy, it may seem callous to hurt him for the sake of hurting him, so "enhanced interrogation" is a nice rationalization. And as long as you are told to do so by an authority figure, many people will comply (as also highlighted by the original Milgram Experiment). Also, many of the proponents for torture have a vested interest in ensuring that it isn't deemed illegal. They would face prosecution should their actions be deemed illegal! That is self-preservation.
I will add, torture IS effective at intimidation, and keeping people "in line" under an authoritative regime. In that respect, there is a great deal of historical evidence (recent history like Saddam, Pinochet, Iran; or older history like the Inquisitions or Roman methods). In that sense, it is a very effective tool, but generally not for the stated purpose of getting reliable information. But it will get a lot of false confessions that can be used for propaganda and other purposes.
INFORMATION BEYOND JUST INITIAL REFUTATION: I just found a HUGE list of quotes as well. Let me go through them and get a few more for you. This is a long list of policy quotes, and people involved in the intelligence fields, so it really won't have a lot of actual research citations to back it up, since researching torture is highly unethical. Although, I think the Stanford Study may be about as close as you can get. My apologies for some of the references, they aren't always the most impartial, or reliable, so anything below this should probably be taken with a grain of salt. And of course, should you want to read it all, the inescapable conclusion is that torture does not work as a reliable interrogation technique, and never has.
According to the Washington Post, the CIA’s top spy – Michael Sulick, head of the CIA’s National Clandestine Service – said that the spy agency has seen no fall-off in intelligence since waterboarding was banned by the Obama administration. “I don’t think we’ve suffered at all from an intelligence standpoint.”
The CIA’s own Inspector General wrote that waterboarding was not “efficacious” in producing information.
A 30-year veteran of CIA’s operations directorate who rose to the most senior managerial ranks (Milton Bearden) says (as quoted by senior CIA agent and Presidential briefer Ray McGovern):
It is irresponsible for any administration not to tell a credible story that would convince critics at home and abroad that this torture has served some useful purpose. This is not just because the old hands overwhelmingly believe that torture doesn’t work — it doesn’t — but also because they know that torture creates more terrorists and fosters more acts of terror than it could possibly neutralize.
A former high-level CIA officer (Philip Giraldi) states:
Many governments that have routinely tortured to obtain information have abandoned the practice when they discovered that other approaches actually worked better for extracting information. Israel prohibited torturing Palestinian terrorist suspects in 1999. Even the German Gestapo stopped torturing French resistance captives when it determined that treating prisoners well actually produced more and better intelligence.
A retired C.I.A. officer who oversaw the interrogation of a high-level detainee in 2002 (Glenn L. Carle) says:
[Coercive techniques] didn’t provide useful, meaningful, trustworthy information…Everyone was deeply concerned and most felt it was un-American and did not work.”
A former top Air Force interrogator who led the team that tracked down Abu Musab al-Zarqawi, who has conducted hundreds of interrogations of high ranking Al Qaida members and supervising more than one thousand, and wrote a book called How to Break a Terrorist writes:
As the senior interrogator in Iraq for a task force charged with hunting down Abu Musab Al Zarqawi, the former Al Qaida leader and mass murderer, I listened time and time again to captured foreign fighters cite the torture and abuse at Abu Ghraib and Guantanamo as their main reason for coming to Iraq to fight. Consider that 90 percent of the suicide bombers in Iraq are these foreign fighters and you can easily conclude that we have lost hundreds, if not thousands, of American lives because of our policy of torture and abuse. But that’s only the past.
Somewhere in the world there are other young Muslims who have joined Al Qaida because we tortured and abused prisoners. These men will certainly carry out future attacks against Americans, either in Iraq, Afghanistan, or possibly even here. And that’s not to mention numerous other Muslims who support Al Qaida, either financially or in other ways, because they are outraged that the United States tortured and abused Muslim prisoners.
In addition, torture and abuse has made us less safe because detainees are less likely to cooperate during interrogations if they don’t trust us. I know from having conducted hundreds of interrogations of high ranking Al Qaida members and supervising more than one thousand, that when a captured Al Qaida member sees us live up to our stated principles they are more willing to negotiate and cooperate with us. When we torture or abuse them, it hardens their resolve and reaffirms why they picked up arms.
He also says:
[Torture is] extremely ineffective, and it’s counter-productive to what we’re trying to accomplish.
When we torture somebody, it hardens their resolve … The information that you get is unreliable. … And even if you do get reliable information, you’re able to stop a terrorist attack, al Qaeda’s then going to use the fact that we torture people to recruit new members.
And he repeats:
I learned in Iraq that the No. 1 reason foreign fighters flocked there to fight were the abuses carried out at Abu Ghraib and Guantanamo.
He said last month:
They don’t want to talk about the long term consequences that cost the lives of Americans…. [The way the U.S. treated its prisoners] was al-Qaeda’s number-one recruiting tool and brought in thousands of foreign fighters who killed American soldiers.
The FBI interrogators who actually interviewed some of the 9/11 suspects say torture didn’t work.
Another FBI interrogator of 9/11 suspects said:
I was in the middle of this, and it’s not true that these [aggressive] techniques were effective.
A third former FBI interrogator — who interrogated Al Qaeda suspects — says categorically that torture does not help collect intelligence. On the other hand he says that torture actually turns people into terrorists.
The FBI warned military interrogators in 2003 that enhanced interrogation techniques are “of questionable effectiveness” and cited a “lack of evidence of [enhanced techniques’] success.
“When long-time FBI director Mueller was asked whether any attacks on America been disrupted thanks to intelligence obtained through “enhanced techniques”, he responded “I don’t believe that has been the case.”
The Senate Armed Services Committee unanimously found that torture doesn’t work, stating:
The administration’s policies concerning [torture] and the resulting controversies damaged our ability to collect accurate intelligence that could save lives, strengthened the hand of our enemies, and compromised our moral authority.
The military agency which actually provided advice on harsh interrogation techniques for use against terrorism suspects warned the Pentagon in 2002 that those techniques would produce “unreliable information.”
General Petraeus says that torture is unnecessary, hurts our national security and violates our American values.
Retired 4-star General Barry McCaffrey – who Schwarzkopf called he hero of Desert Storm – agrees.
The number 2 terrorism expert for the State Department says torture doesn’t work, and just creates more terrorists.
Former Navy Judge Advocate General Admiral John Hutson says:
Fundamentally, those kinds of techniques are ineffective. If the goal is to gain actionable intelligence, and it is, and if that’s important, and it is, then we have to use the techniques that are most effective. Torture is the technique of choice of the lazy, stupid and pseudo-tough.
Army Colonel Stuart Herrington – a military intelligence specialist who interrogated generals under the command of Saddam Hussein and evaluated US detention operations at Guantánamo – notes that the process of obtaining information is hampered, not helped, by practices such as “slapping someone in the face and stripping them naked”.
Herrington and other former US military interrogators say:
We know from experience that it is very difficult to elicit information from a detainee who has been abused. The abuse often only strengthens their resolve and makes it that much harder for an interrogator to find a way to elicit useful information.
Major General Thomas Romig, former Army JAG, said:
If you torture somebody, they’ll tell you anything. I don’t know anybody that is good at interrogation, has done it a lot, that will say that that’s an effective means of getting information. … So I don’t think it’s effective.
Brigadier General David R. Irvine, retired Army Reserve strategic intelligence officer who taught prisoner interrogation and military law for 18 years with the Sixth Army Intelligence School, says torture doesn’t work.
The head of all U.S. intelligence said:
The bottom line is these techniques have hurt our image around the world … The damage they have done to our interests far outweighed whatever benefit they gave us and they are not essential to our national security.
Former counter-terrorism czar Richard A. Clarke says that America’s indefinite detention without trial and abuse of prisoners is a leading Al Qaeda recruiting tool.
A former U.S. interrogator and counterintelligence agent, and Afghanistan veteran said,
Torture puts our troops in danger, torture makes our troops less safe, torture creates terrorists. It’s used so widely as a propaganda tool now in Afghanistan. All too often, detainees have pamphlets on them, depicting what happened at Guantanamo.
The first head of the Department of Homeland Security – Tom Ridge – says we were wrong to torture.
The former British intelligence chairman says that waterboarding didn’t stop terror plots.
A spokesman for the National Security Council (Tommy Vietor) says:
The bottom line is this: If we had some kind of smoking-gun intelligence from waterboarding in 2003, we would have taken out Osama bin Laden in 2003.
The Marines weren’t keen on torture, either.
As Vanity Fair reports:
In researching this article, I spoke to numerous counterterrorist officials from agencies on both sides of the Atlantic. Their conclusion is unanimous: not only have coercive methods failed to generate significant and actionable intelligence, they have also caused the squandering of resources on a massive scale through false leads, chimerical plots, and unnecessary safety alerts…Here, they say, far from exposing a deadly plot, all torture did was lead to more torture of his supposed accomplices while also providing some misleading “information” that boosted the administration’s argument for invading Iraq.
An Army psychologist – Major Paul Burney, Army’s Behavior Science Consulting Team psychologist – said (page 78 & 83):
It was stressed to me time and time again that psychological investigations have proven that harsh interrogations do not work. At best it will get you information that a prisoner thinks you want to hear to make the interrogation stop, but that information is strongly likely to be false.
Interrogation techniques that rely on physical or adverse consequences are likely to garner inaccurate information and create an increased level of resistance…There is no evidence that the level of fear or discomfort evoked by a given technique has any consistent correlation to the volume or quality of information obtained.
An expert on resisting torture – Terrence Russell, JPRA’s manager for research and development and a SERE specialist – said (page 209):
History has shown us that physical pressures are not effective for compelling an individual to give information or to do something’ and are not effective for gaining accurate, actionable intelligence.
Okay, I think that's enough for this answer. I'll try to come back to this from time to time to add references and answers to questions. Keep in mind this is a charged subject, but the main science says it isn't reliable. And even if it were reliable, the ethics would cloud the issue beyond this site's charter I think.