This guy has a 0 feedback rating, won one of my auctions and never paid, never responded to the invoice or a subsequent email. I got my final value fees refunded, but it's still a hassle to go through when this happens.

Anyway, his ID is christ457. If you haven't blocked a bidder before, here's the link to do it: http://pages.ebay.com/services/buyandsell/biddermanagement.html