Chris Bowers is almost entirely correct here; Olympia Snowe isn't going to be a Republican by the time of the 2012 Senate primary. Provided the teabaggers recruit a challenger that motivates the base that challenger will receive the endorsement of every credible 2012 Presidential candidate prior to the primary. They'll have plenty of resources to run a campaign with a Republican-only electorate, which already appears to favor the challenger by substantial margins.
Democrats should seriously consider convincing Snowe (and Susan Collins, while we're at it) to at least become join Joe Lieberman as an independent who caucuses with Democrats. In fact, it might even be useful form a "Mugwump Party" consisting of socially liberal, economically moderate non-Southern Republicans and Democrats: Carper, Specter, Snowe, Collins, Lieberman, Herb Kohl, Jeanne Shaheen, and Dianne Feinstein could all form a little club and get jackets made.