The "legal services" section of Craigslist is a very busy place in most regions of the site. [Craigslist, in case you've been spending the past few years under a rock, is a big classified ads site, split up into a lot of sections.]
That, I suppose, is both a good thing and a bad thing. It's good in that people must be clicking on the ads there if lawyers keep posting. The bad thing is that the site becomes very high maintenance. If you want to keep your ad toward the top of the page, you have to keep posting the ad on the site, often multiple times a day.
In addition, although the posting is free, I'm not sure how many people go looking for a lawyer, in whom they should be able to trust important and valuable secrets, on a site where people can find everything from "casual encounters" to VHS tapes. I suspect that unless your practice or business involves impulsive purchasing decisions, what you see is what you get on Craigslist (and you don't see your ads for long).