I used eBay once...about 700 years ago. Okay, more like 4 or so years ago. I bought an import Depeche Mode CD for my then-fiance for her birthday. I probably overpaid the seller, but it was worth it...and the sale went rather smoothly, other than my m.o. getting lost en route from St. Louis to Toronto.
I will not use it or Half.com anymore though b/c quite frankly, I don't feel comfortable leaving my CC info to someone I don't know.