I use eBay quite a lot, I think it's a great site. You really can find almost anything on there! I mainly use it for collecting records as there's not really any other way for me to get hold of them (them being the rare gems I search so hard to find) but it's also good for random things you can't find anywhere else. My Dad's used my account for little gadgets, things for his motorbike and odd archery contraptions as such. The best things I have ever got from eBay are my Megadeth, Rust In Peace jacket and my signed copy of Death's Scream Bloody Gore.
If you use it properly you will get real bargains at times. If you use it rashly, you'll end up spending a lot of money and possibly regretting it...