I've often thought that literature on alternative medicine makes for great reading, just because there's so much quackery in it. Let me be clear: I'm not thoughtlessly against alternative medicine. Rather, I'm against anything that claims to be medical treatment without solid evidence showing it is safe and beneficial for the conditions it claims to treat.
It's interesting to look at chiropractics from this perspective, especially since a lot of people visit chiropracters regularly (8.75% of the 65,000 respondents in a Consumer Reports poll reported in May 2000). I had a chiropractor as a student, and he ardently believed in what he did (he also had an amazing understanding of human anatomy). Take a tour around the web with Google looking for "chiropractic effectiveness" and you'll find lots of lists of poorly designed studies attempting to support chiropractics.
There appears to be very little solid evidence that chiropractics does much of anything; the single area where it seems to have any scientifically verifiable effect is the relief of lower back pain (e.g. this link). Even for lower back pain, some relatively new meta-studies (here and here) have concluded that chiropractics is not superior to conventional treatments for lower back pain (the Chiropractic News Digest has a nice summary of these two studies and the chiropractic industry's response).
"For patients with acute low back pain, spinal manipulative therapy was superior only to sham therapy (10-mm difference [95% CI, 2 to 17 mm] on a 100-mm visual analogue scale) or therapies judged to be ineffective or even harmful. Spinal manipulative therapy had no statistically or clinically significant advantage over general practitioner care, analgesics, physical therapy, exercises, or back school. Results for patients with chronic low back pain were similar. " (link)and
"A meta-regression analysis of the results of 26 RCTs evaluating spinal manipulation for acute and chronic back pain reported that spinal manipulation was superior to sham therapies and therapies judged to have no evidence of a benefit but was not superior to effective conventional treatments." (link)The second paper quoted above also concluded that massage therapy was effective, while there weren't enough good studies of acupuncture to come to a conclusion. It seems that based on these papers chiropractics is similarly effective to conventional treatments for lower back pain. However, questions of safety still need to be addressed. For instance, see this report that says,
"The most valid studies suggest that about half of all patients will experience adverse events after chiropractic SM [spinal manipulation]. These events are usually mild and transient. No reliable data exist about the incidence of serious adverse events."