This site is German-language, which isn't a problem (I speak German), but aren't most of the users in Europe? I don't think that most of what I want to sell would be worth shipping that far. This isn't virtual merchandise we're talking about, although I'd be happy to sell to Europeans if they want my old books and stuff.
I've used biddingpond successfully and have a couple of other auctions on there going right now.
I'm interested in all of these, but they need to combine and get all of the traffic going to one site.
The ebay of bitcoin needs to establish itself, if for no other reason then so that people can have a way to get money in and out of bitcoin without having to pay exchanges and such.