Actually, SC is very important in the Democratic primary and 47% of the electorate is African-American, so Obama (provided he mobilizes African-American support) can win SC. The general election, however, is another issue. I'm quite sick of the media constantly asking the question of whether he's "black enough." Let's let the voters ask that question if they deem it to be important, and let's let Obama answer the question himself. Instead, the media is constantly framing the candidates as they please to the point where they're driving public opinion of various candidates.
As to the issue of whether there can be an African-American president...I REALLY REALLY hope so. Looking at the electoral map, it seems tough because Obama will have to carry all the Democratic states of last election and get Ohio or another state. And it'd be real tough for him to win Virginia or one of the southern states.
However, for this election, I'm going to hang on to hope, because lord knows if we can't elect an African-American president, we've got some SERIOUS issues, and shouldn't go around preaching democracy to other countries. There's no way we can know unless we really try, and Obama is the best shot at being the first African-American to win office. There has never been a "serious" African-American candidate like him before, so I really hope he can do it. The way I think of it--as long as he can win over the sane-minded Americans, let the racist minority vote for the other candidate.