Yes. Skin colour.
Amongst all the reports about the victory was one with a snippet of a speech made by Martin Luther King. It included this statement:
I have a dream that my four little children will one day live in a nation where they will not be judged by the color of their skin but by the content of their character.
Barack Obama is not being celebrated (or plotted against, it seems) because of his politics, or his gender, but because of the colour of his skin.
Regardless of the reasons that people voted for him, I think the more interesting feature is the reporting of the victory. Why is it such an issue that Obama is black? I can only speculate that it is because the context in which he ran is so horribly racist, deep to the core. Only in a society that has a clear socially dominant class could there be such emphasis on the exception. Suppose that Hillary Clinton was the winner, then gender rather than skin colour or policy would be the distinguishing issue, and would clearly identify the American situation as sexist.
Putting so much focus on the colour of his skin serves only to show that in America, race is still an issue, and that genuine democratic consideration of a candidate's policies plays no part in the mind of the voter.
Note: In the interests of full disclosure, if I was eligible to vote, I would have voted for Obama in order to extract the Republicans from office, and because I think Obama is more likely to implement socially responsible policies.