"White privilege" is NOT the same thing as "socio-economic privilege". Obama has had advantages because of his education, his family's middle class status, and now his own upper-middle-class economic state, but his biraciality does not equal whiteness. As I remember, a law written back in the day would have settled his identity thus: anyone who was at least 1/8 black was considered "black", not "half-white".

Wikipedia sums it up pretty well:

"White privilege is a sociological concept describing advantages enjoyed by white persons beyond what is commonly experienced by the non-white people in those same social spaces (nation, community, workplace, etc.). It differs from racism or prejudice by the fact that a person benefiting from white privilege need not hold racist beliefs themselves."

So whatever advantages Obama has had because of his racial identity, they don't happen because people think he's white.