I've never had anything go wrong with my second hand gear (touch wood). The only things would be a sticky pop up flash on my 20D (which doesn't bother me in the slightest) and I bought a cheap Sigma 28-70mm and it didn't work on either of my bodies (this was my fault, I assumed it would - always check with people who know before committing to buying).
My thinking is, that most photographers don't spend a heck of a lot of money on gear and trash it, so it should be well looked after (maybe not if it was used by a pro though). But the guy I bought my 20D from was a pro and it did everything I needed it to, and it's still going strong today. The gear is built to last (perhaps not the shutters though!).
Ebay's policy seems to strongly favour the buyer so I've never thought twice about buying used from them.
One consideration with second hand bodies is the shutter life. With some cameras you can find out how many times the shutter has clicked, but not on all of them. So it might have a shorter life. But shutters can be replaced. If you're good with manual work and confident enough you can do it yourself, otherwise it'll cost a bit to get it replaced for you. How much I don't know, I've never had to do it yet.
Think about the glass more than the body though, the glass really is the limiting factor on your image quality.
Have fun looking! I always enjoy looking for new gear, but not at my bank balance!