The indispensible Dan Kennedy rises to the defense of polls:

Six weeks ago, as we all know, John Kerry's presidential campaign was dead in the water. As Dan Aykroyd's Bob Dole would say, he knew it, we knew it, and the American people knew it. Fundraising dried up. He poured his personal money into the campaign in a desperate attempt to stave off collapse. It got so bad that in New Hampshire, which is close to a must-win state for him, the alternative to Howard Dean increasingly came to be seen not as Kerry but as Wesley Clark.

Now, what if Kerry had ignored the polls? Guess what: he'd be limping into the final week of his campaign. Instead, he shook up his campaign staff. He sharpened his stump speech. And - most important - he pulled up stakes in New Hampshire in favor of running full-time in Iowa during the last few weeks before the Iowa caucuses.
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In other words, it appears that the polls were an accurate reflection of what was happening on any given day. The polls were immensely useful to the Kerry campaign. Where the pundits blew it was in taking those polls and using them to predict what would happen two or more months out. But even here I think it would be wrong to be too harsh. No one has ever come back from the kind of hole Kerry had dug himself into.