At 1:30 or so of this clip, what looks like footage from The Beatles: Rock Band goes up on the screen behind Sir Paul McCartney, performing at Coachella on Friday.
The clip is 9 minutes long, but of the ones circulating out there, it offers the longest and clearest look at Rock Band's animations. Which it has to be, the face texturing and the cuts have that RB feel.
Update: This has been confirmed on McCartney's Web site:
it was a night of firsts and was the unexpected, unannounced world premiere of the images from the coming Beatle Rock Band game
Destructoid was tipped to another clip here, which is shorter, but is of the same set - "Got to Get You Into My Life." Tons (sigh tonnes) of people have camcorders up in the air filming the screen, making this, what, a GDC presentation or something?
You know, if this game doesn't have unlockable Pete Best and Yoko ... oh forget it, like it ever would ...
Paul McCartney Coachella 2009 Front and Centre 1st Beatles Rockband Footage [YouTube, thanks Adam K. Lee N. and Nick C.]