Back in the early 1990s, Gary Mauser (Simon Fraser University, British Columbia) and I wrote an article, originally published in Political Communication & Persuasion, explaining why polls are sometimes inaccurate as measures of public opinion. The article is titled 'Sorry, Wrong Number': Why Media Polls on Gun Control are So Often Unreliable, and although the focus is on polls about gun control, the article observes some general problems with polling. If Senator Obama on election day significantly underperforms, or overperforms, what the polls predict, there will be many possible causes, other than the "Bradley Effect" or the "Reverse Bradley Effect." There are many factors, other than race-consciousness of the interviewees, which may cause a gap between opinion polls and actual votes.
Some Reasons Why Polls May Be Inaccurate