(Don't be sure that John Edwards' dropping out, benefits Hillary Clinton. Edwards, by the way, according to the AP*, is not endorsing anyone right away.)
The question as polls closed was two-fold: whether that margin would hold on primary day, and whether Obama's increasing appeal among black voters would come at the expense of support from whites, who had said in surveys that they preferred Clinton and Edwards.
Obama answered today: His margin of victory among blacks was far higher than polls had anticipated; Obama beat Clinton among African-American women by a whopping 65 percentage points, exit polling data showed. But Obama also won a quarter of white voters, and nearly tied Clinton among white men. Clinton performed best among white women, winning 42 percent to Edwards's 35 percent and Obama's 22 percent.
http://www.boston.com/news/politics/politicalintelligence/2008/01/obama_wins_sout.html*The former North Carolina senator will not immediately endorse either candidate in what is now a two-person race for the Democratic nomination, said one adviser, who spoke on a condition of anonymity in advance of the announcement.
http://www.politico.com/news/stories/0108/8203.html