First off, I am not a lawyer, and I do not play one on the 'net. This isn't anything remotely like legal advice, assuming I could even provide such a thing.
Secondly, although I am an employee of Stack Exchange, I'm not writing this on their behalf (i.e., I didn't ask Robert to pre-approve this).
Okay, given that…
The important issues here are
The article A Quagmire of Internet Ethics Law and the ABA Guidelines for Legal Website Providers, by Margaret Hensler Nicholls, says (section III.C, D):
UNAUTHORIZED PRACTICE OF LAW
The unauthorized practice of law consists of providing legal advice in a jurisdiction where a person is not admitted to practice law; lawyers must not violate states’ rules on unauthorized practice. The Internet raises the threat of unauthorized practice of law occurrences because lawyers communicate more frequently and easily (often unknowingly) with people outside their licensed jurisdictions. Because an attorney may not be aware of the potential client’s domicile, the attorney may provide incorrect advice based on the wrong jurisdiction’s law.
The threat of lay people giving legal advice without any license is even more concerning. As mentioned above, many non-lawyers create and maintain legal websites. These providers believe they offer legal services for less, and consumers either ignore their lack of pedigree or prefer the lower cost. Non-lawyers have been found to have engaged in the unauthorized practice of law with legal websites. In an Ohio Board of Commissioners on the Unauthorized Practice of Law decision, the court found an unauthorized practice when Palmer, a non-lawyer, offered legal advice through his website “amoralethics.com,” which boasted “Free Legal Advice” and elicited questions on legal matters. Online legal forms and software hosted by non-lawyers also pose difficulty; online wills, divorces, and contractual agreements exude an “air of reliability about the documents, which increases the likelihood that an individual user will be misled into relying on them.”
Attorneys may trigger attorney-client relationships and potential conflicts more easily based on website interaction. The anonymity of the Internet contributes to this increased likelihood of attorney-client relationship problems. An attorney-client relationship develops when a lawyer gives specific legal advice to a person, consents to providing legal advice, or fails to decline a person’s request, knowing the person reasonably relies on the lawyer. E-mail communication and online referrals can attach a duty as “Model Rule 1.18 gives prospective clients protection where the attorney-client privilege has not yet descended, but the information the prospective client has provided to the lawyer should nonetheless be considered confidential.” Yet, the Model Rules do not specifically address the existence of attorney-client relationships over the Internet. Again, lawyers face uncertainty in ethics regulation. In turn, this problem impacts the consumer who may rely on a lawyer in an ambiguous situation, given the anonymous nature of the Internet and its lack of spatial and temporal boundaries.
From The Ethics of Practicing Law in Cyberspace by Jennifer P. Hopkins (Section III):
Can a Disclaimer Prevent a Lawyer-Client Relationship?
Many legal web sites use a disclaimer to attempt to prevent a lawyer-client relationship. "Indeed, much of the legal advice-giving activity online seems to hinge on the belief that blanket use of disclaimers will protect lawyers against all risks associated with their conduct." But online disclaimers may not provide the protection that many lawyers would hope. …
Even if a lawyer did create a disclaimer that potential clients read and to which they signaled their consent, the question remains whether such a disclaimer would be permissible.
Indeed, if disclaimers could be so easily utilized, a lawyer could avoid the prospect of malpractice liability, or even the reach of most ethics rules, simply by expressly disclaiming the intent to create an attorney-client relationship with anyone… At some point the conduct of the lawyer would be so inconsistent with the disclaimer of a professional relationship that the disclaimer would be treated as ineffective.
Three states have already ruled that disclaimers will not avoid lawyer-client relationships in the context of 900-number telephone services to provide legal advice. "A lawyer operating a '900' pay-for-information telephone number by which callers are given legal information ... enters into a lawyer-client relationship with the caller and may not avoid it by disclaimer." The validity of a disclaimer is likely to be measured against the lawyer's conduct, depending "in part on the extensiveness of the advice sought and the fact-intensiveness of the answer given by the attorney."
(aka the "TL;DR" section)
If you're a lawyer: the American Bar Association has Model Rules of Professional Conduct that define attorney-client relationships. These have been adopted by 49 states.
Whether you're a lawyer or not: You can get in trouble for Unauthorized Practice of Law.
Both of these can be criminal and/or felony offenses.