I have personally not bought a computer off of ebay but I know someone who did, and the computer worked just fine. I have however, ordered one off Amazon, in fact its the one I'm using right now and I have had it for almost two years now. I can understand some of the apprehension people have in doing this though, because I have been burned when it came to buying a printer online from ebay. The only advice that I can give you is find out what you can about the auction and the seller before buying. Even if you have to send an email to the seller, if they are legitimate and want to make this sell they will take the time to answer your questions. Also, find out what kind of rating these seller has received in the past, as well as the feedback they got this can tell you if they had satisfied customers in the past as well.
No, I never have and I don't think that I would. There are some things I'd just be too hesitant getting from ebay, though it can be great for many things. Electronics I shy away from there.
If it was dirt cheap, as in <$100, looked like it was in good shape in the pictures, and had decent hardware specs - I think that would minimize your risks. Worse case scenario, you may need to reformat it and install one of your own copies of Windows on it. I'm actually considering selling an old laptop of mine on eBay, I just got to get around to reformatting the whole thing and getting all the drivers reinstalled.
We have bought a laptop for my father-in-law last year in ebay. But we have to look for a seller/company that has a very good reputation. Not worth it buying from someone who only has a few reviews. They must really be very trusted sellers as the items we'd buy is not that a small amount of money. Anyway, we bought it at around £300 brand new and great specs. It was delivered to the house just after 2 days of ordering it by a well known courier. Much to say, everything went well.
I have done this quite a few times over the years and I have never had a problem with any of them, I normally buy refurbished computers which are rather nippy but at a great price. It is always a good idea to have a look around first though, don't buy the first one you look at.
Major purchases for me I just have to buy from a brick and mortar store. I have far too many questions to have to chat with someone online and I want to know that I can bring it to the store if I have problems with it. That being said I would never buy a computer on eBay. There are just too many unknowns and I'm paranoid about my warranty which is next to NIL when you get stuff from eBay.
