I actually doubt that Obama's position on gay marriage is really going to be all that big of an issue.
No dude, there are plenty of right-wing Christians who will base their vote solely on someone's stance on Abortion and Gay Marriage. That is a fact.
It goes both ways too, though. My biggest gripe about the gay community is that they only care about their own. There's no doubt most of them will vote solely based on someone's stance on Gay Marriage as well. And that's wrong. It's far from being the most important issue, including to those who are gay.