They are the only real game out there. Good and bad. I've had very poor luck with Craigslist. Because of its no fee ad placement, many throw there stuff on it with no real intent to follow through with the sale. I looked for a used mountain bike and a large screen TV on CL and I would say out of 10 inquiries, 25% replied back. And that may of been a week or so later. Never completed a deal. I guess if your looking for a nude massage it works out.
I've found Ebay to be good as long as your interest in buying or selling focuses on a particular group. When selling Porsche items, I've had great success because I feel like they are similar in interest and all around honest people. When I venture into more main stream interest, (TV monitors, Mp3 players), then I run into the problems of those trying to make a quick buck. All in all, Ebay has worked for me.