It seems to have some acceptance in the gaming industry (a .biz name I sold a while back became a popular games industry business news/community site, and it's not the only big site of that type on a .biz.)
Overstock getting o dot biz isn't going to hurt the extension any. If a few other high-profile businesses follow suit it could definitely increase interest in the extension. While there are some situations where it really sounds bad (imo, medical/legal/professional - legal .biz names especially sound like ambulance chasers to me!) the biggest problem with the tld is that the average person is unfamiliar with it and doesn't "trust" it. Get a few legitimate, name-brand companies to use it, throw in some marketing and that could change.
The other 4 missing from the auction are 0, 3, Q and I. Anyone guesses who might be in the running for them?
(I think they should just give e.biz to me :D!)