This article summed it up nicely. Here's Obama speaking with Rick Warren:
Rev. Warren: "Define marriage."
Sen. Obama: "I believe that marriage is the union between a man and a woman. Now, for me as a Christian, it's also a sacred union. You know, God's in the mix."
Rev. Warren: "Would you support a constitutional amendment with that definition?"
Sen. Obama: "No, I would not."
Rev. Warren: "Why not?"
Sen. Obama: "Because historically, we have not defined marriage in our Constitution. ... I am not somebody who promotes same-sex marriage, but I do believe in civil unions."
As the article says, there is very little difference between Obama's statement and what Miss California had to say.
I think Ms. Prejean was by far the bravest of the two. "She was being questioned by a gay judge and a gay-friendly jury, after all. She surely knew that the response of her heart was not the answer this audience was looking for. Obama, on the other hand, was speaking before a largely conservative audience in an evangelical church when he endorsed the traditional view of marriage. How hard was that?"
I don't have a problem with gay marriage. Gay marriage doesn't threaten my marriage or my relationship. I think the best way to resolve this controversy is to get the government out of the marriage business altogether. Have everyone register their civil unions, and have these unions form the basis of any societal rights that marriage confers now. And if a church wants to "marry" someone officially, then that's great. I don't think any church should be forced to perform a marriage ceremony if it is against their own doctrine. That way, everyone is on an equal footing.