Even on some things that I had reservations about buying.
That said, there are some things I would likely never buy on ebay, like guitars for example. I want to touch it/play it before I buy it. Can't do that on ebay (yet).
PC parts (buy/sell), auto parts (buy for friends hopping up Acuras)...been using it for 4+ years on a regular basis. I bought my entire home theater system on a combination of ubid/ebay and haven't had any issues with it. In fact, the ONKYO amp was bought on ebay...the supplier was Crazy Eddy's in NY.