I believe that Joe Lieberman was also a poor choice. Even back in 2000, a lot of liberals (myself included) strongly disliked him, so putting him on the ticket likely depressed enthusiasm among the base, and may even have driven enough lefties into the arms of Ralph Nader to throw the election.As someone who got caught up in the Nader fiasco in 2000, Gore could have done himself a huge favor if he had picked a genuine progressive as his running mate. Gore was running as somewhat of a centrist, and his selection of Lieberman only reaffirmed that image. If Gore had chosen someone who had a lot of credibility in the progressive community, much of that Nader zeitgeist would have been squashed. The Republicans, on the other hand, seemed to understand that appealing to the base had merit and weren't afraid to have a rock-ribbed conservative as the VP.
I don't think Obama has the same problem with the base that Gore does, nevertheless I think it would be a poor decision to go with someone that the progressive community has issues with.