Rock band 2's already out on 360 and PS3, but the other versions - Wii and PS2 - are running a little behind schedule. So far, in fact, that they're still not out yet.
But they're coming! Or, at least, the Wii version is. A very public, very humble announcement on Harmonix's site says that Rock Band 2 on the Wii will be shipping on December 18, meaning that, if you're lucky, it'll arrive in stores just before Christmas.
That's cutting it pretty fine, but if it's any consolation, Harmonix are very, very sorry, and would like "to apologise for the delay in getting RB2 onto the Wii and to reaffirm that we believe that Wii is an amazing and unique fit for Rock Band 2, and one that we care deeply about getting right."
Wii Rock Band 2: Response [Harmonix]