I think Thomas Friedman has his finger on the reason why I, and probably more than few others, voted the way we did this year. The election was not about McCain and Obama or their foreign policies or even their economic policies. It was about repudiating the Bush administration:
[They] knew that after the abysmal performance of the Bush team, there had to be consequences for the Republican Party. Electing McCain now would have, in some way, meant rewarding incompetence. It would have made a mockery of accountability in government and unleashed a wave of cynicism in America that would have been deeply corrosive.
It's the reason I would have voted for San Francisco's Measure R. The name "George W. Bush" must be widely discredited for all posterity, that policies like his may be avoided in the future.
Not a completely rational reason to vote, but so little about politics is rational anyway.