Fickle Voters and Other Frights That Pollsters Dread

From the Conservative (and Rupert Murdoch owned) London Times:

"Every pollster is predicting a victory for Barack Obama. Might a grinning John McCain be pictured on Wednesday triumphantly holding a pile of incorrect polling data? // There are two things that say that he might. In an election where only 60 per cent may vote, all pollsters have to weigh their findings to reflect how likely respondents are to cast their ballot. The difficulty is deciding how. Usually pollsters use previous elections to help them to decide who is going to vote. But what if, in this election, different sorts of voters are going to turn out?"
Fickle voters and other frights that pollsters dread - Times Online