With virtually everyone else sounding off on this subject, I thought I'd add my two cents worth.
Okay, Tim Kaine's record of accomplishment as Governor has been...what? However, he strikes me as a decent guy, and it wouldn't hurt to have a sane Virginian (read: not Mark Warner!) in the Old Executive Office Building. Even if you don't like Barack Obama, it doesn't hurt to hedge your bet in case he does win.
Therefore, if Obama wants Kaine, I'd be happy with the choice.