I think the Maine Senate race will be interesting. There is no other way to describe it; any race is interesting obviously but I really think it could surprise a lot of people. Regardless of her popularity, Collins has never won big margins. Look at 2002; a good Republican year, popular as ever and facing an unknown opponent. She won with less than 60% of the vote. I think at the very least Allen will reduce her from 58%-42%. Also, Maine has a history of taking down popular Senators - Margaret Chase Smith in 1972 is an example. Her opponent went down heavily in 1978 as well.
I'd vote Allen. No surprise there.
But if Collins won, I wouldn't be terribly disappointed. She's a decent Senator.