The question "is chiropractic treatment effective?" is quite wide, as this type of treatment is proposed for several different illnesses, from neck or back pain to headache even to gastrointestinal problems.
Furthermore, as for many alternative treatments, they are often proposed by a wide variety of persons, from people with medical degrees (more or less related to the field), to people who attended chiropractic colleges, to charlatans... and obviously the results (and the side effects) vary accordingly.
Now, you cited two Wikipedia links that analyze negative effects of this type of treatment.
The 2009 study is a bit misinterpreted in Wikipedia as it refers to spinal injuries in students of a chiropractic college.
Prevalence of musculoskeletal injuries sustained by students while attending a chiropractic college.
Although we cannot conclude much about the efficacy of the treatment from this study (as it was administered by students), it clearly proves the point that an uncompetent chiropracter can harm his/her patient.
From the conclusions of the paper (parts in italics are my additions)
This study shows that some students who enroll in a chiropractic college with preexisting injuries can have these injuries exacerbated during training. A recognizable amount of new incidences are possible as a result of the adjustments they administer or receive from other students. The most prevalent injuries from receiving adjustments occur to N/S [neck-shoulder], whereas those due to administering adjustment occur to H/W [hand-wrist]. Only a few of the injuries sustained in college were severe to the extent of inhibiting the performances of normal daily work.
Some other severe side effects of chiropractic treatments have also been reported
Acute spinal epidural haematoma causing cord compression after chiropractic neck manipulation: an under-recognised serious hazard?
Bilateral vertebral artery dissection after chiropractic maneuver.
Simultaneous bilateral internal carotid and vertebral artery dissection following chiropractic manipulation: case report and review of the literature.
Note that this are very serious side effects, which are clearly not acceptable in a risk-benefit balance for treating neck-ache or similar problems.
We should, however, also consider that -although very serious- these side effects are generally rare. As the first of these three papers concludes:
Spinal manipulation is a treatment performed by chiropractors, some orthopaedic surgeons and general practitioners in the UK. It is clear that the rarity of traumatic spinal epidural haematoma makes it difficult to establish cause-and-effect connections though the potential serious risks of high-spinal manipulations, however small and including vertebral artery dissection, should be communicated and discussed during consenting of patients.
A similar conclusion was drawn by a 2003 literature meta-analysis, which was inconclusive regarding artery dissection:
Association of internal carotid artery dissection and chiropractic manipulation.
The medical literature does not support a clear causal relationship between CMT and ICAD. Reported cases are exceedingly scarce, and none support clear cause and effect.
Furthremore, a 2005 literature meta-analysis states that
Perceived causation of reported cases of cervical artery dissection is more frequently attributed to chiropractic manipulative therapy procedures than to motor vehicle collision related injuries, even though the comparative biomechanical evidence makes such causation unlikely. The direct evidence suggests that the healthy vertebral artery is not at risk from properly performed chiropractic manipulative procedures.
Cervical artery dissection. A comparison of highly dynamic mechanisms: manipulation versus motor vehicle collision
Another recent (2011) study showed minimal effects on chest deformation using a dummy as a test subject
An experimental study of chest compression during chiropractic manipulation of the thoracic spine using an anthropomorphic test device.
So, do these treatment have any efficacy that can justify the risk of these (albeit rare) side effects?
Several randomized clinical trials have shown the inefficacy of chiropractic treatment for muscoloskeletal pain. They're reviewed here:
Osteopathy for musculoskeletal pain patients: a systematic review of randomized controlled trials.
Eleven RCTs indicated that osteopathy compared to controls generates no change in musculoskeletal pain. Collectively, these data fail to produce compelling evidence for the effectiveness of osteopathy as a treatment of musculoskeletal pain.
Also, regarding gastrointestinal problems the efficacy of chiropractic treatment could not be proven
Chiropractic treatment for gastrointestinal problems: a systematic review of clinical trials.
Only two trials were found--one was a pilot study, and the other had reached a positive conclusion; however, both had serious methodological flaws. There is no supportive evidence that chiropractic is an effective treatment for gastrointestinal disorders.
Finally, the 2010 study linked by Wikipedia, which analyzes deaths after chiropractic treatment.
Deaths after chiropractic: a review of published cases.
From the article
Twenty six fatalities were published in the medical literature and many more might have remained unpublished. The alleged pathology usually was a vascular accident involving the dissection of a vertebral artery
and (bold is mine)
In conclusion, numerous deaths have been associated with chiropractic neck manipulations. There are reasons to suspect that under-reporting is substantial and reliable incidence figures do not exist. The risks of chiropractic neck manipulations by far outweigh their benefits. Healthcare professionals should advise the public accordingly.