My backside is parked on a couch I bought from craigslist (Austin) and I'm completely happy with it. I've never tried to buy any PC hardware from the list, but it sounds like you're the one following up on 'too good to be true' ads. If the seller doesn't provide enough detail you can email them and ask for more, or just ignore it. WRT to furniture, I simply ignore postings that don't include a picture.
For a "spectacular failure" it sure gets a lot of postings every day, in an awful lot of cities. Personally I think it's going to kill the traditional 'pay' market for classifieds. The alternative weekly here has already started offering free classifieds.