Just got off the phone with a chiropractor in Colorado Springs who wanted to know whether or not domains names effected search engine rankings. The short answer is, yet they do.
The long answer goes something like this: your domain name is the first thing search engines see when they find your website and they assume that a website called "discountsneakers.com" probably sells discount sneakers and not automotive parts. At the same time, search engines also realize that not every discount sneaker store can name their website "discountsneakers.com". When a search engine like Google is looking at a website, they categorize a website according to the following pieces of information (roughly in order of importance):
H2, H3, etc
As you can see, the domain name ranks pretty low on this list but it can make a difference if you have a highly competitive keyword. The domain name by itself doesn't do that much but it seems to magnify any related keywords on the rest of the website. For example: having the domain ChiropractorsInSeattle.com doesn't guarantee that your website will rank well for "chiropractors in seattle" but it does seem to make it easier to rank #1 for that search if you add lots of content that includes that keyphrase.
If you have the opportunity to use a domain that includes your geographic area or the words chiropractic/chiropractor, you should jump on it. If you don't have that option, don't sweat it because the effects are relatively small and you can still beat the competition by creating better content and building better backlinks.
One last note: chiropractors often ask me whether or not they should buy multiple domain names for their website. For example, one chiropractor wanted to buy "ChiropractorInTuvalu.com", "ChiropracticTuvalu.com", and "TuvaluChiropractors.com". His rationale was that he would rank better if he had lots of keyword rich domain names pointing to his website. Unfortunately, Google is smarter than that and knows that you're just pointing a bunch of domain names to one website. All of the extra domain names are worthless and will be ignored by Google.
There's your chiropractic marketing tip of the day!