Pollster.com
Highlights possible theories for why the polls between Iowa and New Hampshire predicted the NH outcome so poorly on the Democratic side. Given all the choices, I go for this explanation: undecided voters at the end - many of whom were picking Clinton in pre-Iowa polls when she had a big lead - were not significantly covered in media reports of the polls, neither was the softness of Obama's support. (The same polls everyone's whining about being so wrong did warn that there were 20% undecided and 30% of Obama's supporters saying they could change their mind.) People deciding on the last day went (back) to Clinton.

No, that doesn't make me feel any better, but it does make some sense. The stories about Hillary under attack for getting choked up simply came later, and swayed more voters, than the story of Obama's surge. It resonated.