Do you like Rock Band Unplugged? Do you like ... buying a new PSP? If so, you'll be pleased to hear this. According to Destructoid, Best Buy's PSP Go listing mentioned a free voucher for a download of Rock Band Unplugged. If it was in the listing, it has since been removed. We've contacted Sony to determine the truth of this rumor.
If this turns out to be true, then the PSP Go won't cost $80 more than a PSP -- it'll just cost $50 more than a PSP Rock Band Unplugged Entertainment Pack, which sounds better. The existence of a current PSP/Rock Band bundle makes this more plausible, as well.
Update: Looks like the PSP Go will only be bundled with a Rock Band Unplugged demo -- not the full game, as seen by this image from thatgamecompany's forums.