I post as well as seek ads on Craigslists. In the last six months I got one good client, a professor in TN. As far as responding to ads, I've gotten a few customers for one time projects.
I think with Craigslist the thing is those that advertise there are usually looking for affordable services, so with leads from this site I'm a usually more flexible with my pricing. I will also caution you to be careful and get all payments upfront or at least before releasing the finished product. If using PayPal to collect I also strongly advise waiting 3 to 4 days after receiving payment to release the finished project, even for credit cards.
Hope this helps.