He won't hurt anybody, because he has almost no support left. In 2004, he got 0.82% in Connecticut; in 2008, he got 1.16%. He will do nothing in 2010, even if he does run.
But, if he just ran for a statewide office, he'd be spending a lot more time in the state, something he didn't do when running for President.
That being said, I think he'd break 5% easily. Maybe even 10-15% if he's lucky. He has the name recognition down.
Name recognition for him is not a positive. He is reviled among Democrats.