Not sure if this is the "biggest surprise premiere in VGA history" we've been promised, but MTV put up a "Green Day: Rock Band" video dated three days into the future, then pulled it. Embed code still works, though.
As you can see, the band's rocking out to "American Idiot" with note highways, band shots, the works. And then as if to drive home the point, the title card Green Day: Rock Band slams over it at the end. Sounds rather definite to me. I guess we shall know if this is for-sure real or not in about 90 minutes, right?