Although Barack Obama has said that he supports civil unions, he is against gay marriage. In an interview with the Chicago Daily Tribune, Obama said, "I'm a Christian. And so, although I try not to have my religious beliefs dominate or determine my political views on this issue, I do believe that tradition, and my religious beliefs say that marriage is something sanctified between a man and a woman."
Several liberal politicians and gay marraige advocates are upset by Obama including Rick Warren in the inaugural festivities. A couple of them seemed to say (sorry, not link or quotes) that Obama was in favor of gay marriage and that is why Warren's inclusion was such a shock to them.
Byron York over at NRO offers a list of Obama's actions and positions that seem to give them hope:
[W]hy are gay groups so angry, knowing that Obama opposes gay marriage? In the end, it seems that the reason for the anger is that, no matter what Obama says, a number of gay activists appear to believe the president-elect is, deep down, with them on the issue. “He’s stated his support for the repeal of the Defense of Marriage Act, he spoke out against Proposition 8, he’s against the Federal Marriage Amendment, he’s for full civil unions and domestic partnerships, he’s for the repeal of Don’t-Ask-Don’t-Tell,” [Human Rights Campaign spokesman Brad] Luna said. “He’s with us on all the issues of concern to our community except classifying relationships with the term marriage.” So what if Obama says he believes marriage is between one man and one woman; his positions, especially his support of repealing the Defense of Marriage Act, seem to suggest otherwise.
If it walks like a duck ....