As long as we're all throwing out speculative theories for why the good people of New Hampshire voted the way they did, let me add one more. One thing that's become clear is that many of us in the press probably were unduly influenced in our analysis by the memory of what happened in 2004, when Kerry's victory in Iowa catapulted him into the lead in New Hampshire and he never looked back.
A lot of New Hampshire voters realized the degree to which they simply echoed the Iowa results. I did some door-to-door canvassing in the state, both in the primary and general election, as a bright-eyed college student, and I talked to a couple people who were sort of jealous that Iowa seemed to have more influence than they did. (I know, I know, it's absurd for people in New Hampshire to complain about a lack of influence in the process, but it's what they were saying.) It's entirely possible, especially given the fawning media treatment Obama's received over the last few days, that New Hampshire residents simply decided they didn't want to be a rubber stamp for the Hawkeye State again. (At least that's a less disturbing explanation than the much-discussed Bradley effect.)
Of course, there's also the possibility that voters thought Hillary was just a better candidate on the merits, but that's such a boring explanation!