Maybe more people like Sununu now.
I doubt that's the reason.
If this poll is legit, or at least close enough such that Sununu is in the lead (it's hard for an indy poll to be off by 20 points), I'd estimate it's because New Hampshire is intensely focusing on the 2008 Presidential contest.
What does that mean? Well, it means New Hampshire, more than anywhere else, has already put the Bush administration behind them and are instead focusing on the new crop of Republicans. If you're excited about Rudy, or McCain, or maybe even Huckabee, you're not focusing on the past failures of Republicans. You're focused on the future.
And it's the past failures of Republicans that mainly put Democrats into the driver's seat in New Hampshire.
Truth be told, it will be a real challenge for Democrats to make 2008 about Bush. It's just not the natural way people think.