I buy lots of things on E-bay, and I also sold a car and a computer on there.
My rule of thumb for buying on ebay: if it's something I can buy locally and the price is comparable, I buy it locally. If it's something unusual that I can't find locally, I consider buying it on ebay. I have several friends who were ripped off hundreds of dollars with electronics purchases made on ebay.
A few years ago, I bought an extra copy of a mag called BIKINI that had actress Rebecca Gayheart on the cover. It had lots of the then-hot young female film stars like Gayheart, Jaime Pressly, Charisma Carpenter and others in bathing suit shots. I put my extra copy up for sale on eBay at an initial price of something like $5, hoping to maybe double the cover price. Before it even got really started, I got an email from a guy who worked at a museum in NYC; he wanted a copy to display and couldn't find one. He offered me $75 on the spot. I got an official museum check a few days later. True story. :)