As far as race is concerned, Obama carries himself and communicates more like an affluent white American than have any of the other candidates, Republican or Democrat, thus far.
Need proof? Go to a store, walk down the street, turn on the television, and count how many African American people you see who dress, move, and talk like him. Unless you're in an affluent neighborhood and/or observing an adult black male with an income as a professional greater than 150k+, the likelihood of catching sight of such a person is nil.
Though Jesse Jackson and Al Sharpton have been better representatives of black culture in terms of speech and manor of expression to date, Obama has mastered his demeanor to bypass the gag reflex of white America; the knee jerk reaction that many other black people, intentionally or otherwise, through their quest for individual expression and through action toward establishing themselves in their social hierarchy, consistently trigger.
Now for the obligatory disclaimer:
Clearly these observations sound racist but in no way are they meant as so. I hold every facet of cultural representation under similar curious scrutiny as I feel that it is healthy to question.