The choice in 2008 may not be between a historic vote for a "black" or a woman candidate and a vote for another white guy, it may be between symbolic and concrete progress. Electing Obama or Clinton would be an amazing symbolic triumph, but putting a black or female face in the White House doesn't necessarily do anything for the concrete living conditions of black Americans and women.
Because these groups are disproportionately poor, the quickest way to make a real difference for them is to reduce class inequality. And only Edwards is making class inequality a central part of his platform. So, ironically, the best choice for blacks and women may be the white guy.
Of course, I'd like to see both symbolic and concrete progress, but it looks like we're going to have to choose. In that case, it's not obvious to me that symbolic progress wins out over a concrete improvement in the daily lives of the groups that Obama and Clinton represent. What do you think?