The smart money is on Tim Kaine for Democratic VP. I see Barack as insecure and consumed by image. As Kaine is shorter, fatter, with worse hair, Obama would be comfortable around him.
He could defend the Kaine decision as a strategic counter to the Paris and Britney commercial, but it would really be all about Obama and his self-image.
Update: Missed that one. The hair-plugs are probably reassuring though. Biden should make it a fun election to watch.