The results tended to correlate with the black population in a state: blacks made up 15 percent or more of the population in almost all the states where the polls showed less support for Mr. Obama than there actually was; in the three states where polls showed more support than there was, less than 10 percent of the population is black.
The differences are too great to be explained by just high black turnout, said Anthony Greenwald, one of the researchers. Nor were people necessarily lying. Instead, he sees a cultural dynamic at work: the states where polls underpredicted support for Mr. Obama were generally in the Southeast, where the culture has more stubbornly favored whites, so the “right” answer there was to choose the white candidate. In the three states where polls in the study overpredicted support for Mr. Obama — Rhode Island, California and New Hampshire — “the desirable thing is to appear unbiased and unprejudiced,” Mr. Greenwald said. (Many polling experts also believe that Mr. Obama was benefiting from an Iowa bounce in the late New Hampshire polls, as Senator Hillary Rodham Clinton had been ahead for months, and that therefore Mr. Obama’s loss there was not a true Bradley effect.)
I don't know about this. Here's the data. I think the NH/MA/RI "Bradley effect" quite possibly existed, but was more specific -- i.e. it had to do with the sense that Obama is like Deval Patrick, which he is -- than general racism. Note that Obama overperformed in CT and NY state. MA/RI aren't in play even with a Bradley effect, NH I wouldn't count on. As for the reverse B.E. in the south, I think the deal is that all the white racists there are Republicans, and Obama outperformed among black people. I really don't buy the closet white liberal theory.
It isn't about black turnout so much as margins. All over the south, 40-60% of Dems are black. The difference between Obama winning 85% of the black vote and 95% -- which the media treat as equivalent -- is quite substantial, it's a five-point boost overall. See Jay Cost's old post for more.