All 4 of my bikes I bought used, and I love them all (equally--or so I tell them ). One from the LBS, one from a friend (it was too big for her), and the other 2 off Craigslist. One was not ridden due to the owner having a baby, and the other belonged to an ex-wife.

I've been quite happy with the Craigslist experience, and I wouldn't hesitate to buy a bike off it again. And actually I'll browse a couple times a week (even though I'm not looking for another bike) just in case my dream bike might be posted.