This whole notion of masses of people "excited about a black president,"in particular, ignores the fact that since 1984, we've had a black person at least declare for president every year. In 2004 we had two--a black man and a black woman. I don't recall there being much excitement around the notion of President Al Sharpton, amongst blacks or whites. It's true that there is a great deal of excitement now about electing a black president--but that's because the prospect is Barack Obama. Ditto for Hillary.
This idea that Blacks are mindlessly flocking to Obama because he's a Black face (or women, to a lesser extent, for Clinton) is unbelievably patronizing to everyone involved. Blacks have proven themselves to be more than willing to vote for White candidates -- including against other Blacks (recall that Clinton lead Obama amongst Blacks early in this campaign). Same with women. Same with Black women for that matter (Carol Mosley-Braun all the way!). It is Whites and men who have historically shown far more ... reticence at straying from the bounds of identity politics over America's electoral history. The reason we see high support for Obama and Clinton is because they are both fantastic candidates.
Given that it seems Blacks and women have been far more willing to evaluate candidates "on the merits" than Whites and men, perhaps, come the general, we might deign to wonder as to the cause if Whites (I'm assuming Obama will be the nominee at this point) don't follow along. Who has shown the more neutral, dispassionate judgment in the past?