Last year, Snowe voted with Republicans just 57% of the time when a vote divided the parties, and (with her fellow Mainer Susan Collins) was one of the few voices on either side of the aisle willing to buck the party.
Even if it means Democrats have a chance to pick up a vote in a year where this seat could literally sway the balance of power in the Senate, I'm far from happy to hear this. I might lean left more than they do, but I firmly believe that moderates are an integral part of our political process. With Snowe's retirement, there is now an appalling shortage of independent voices on Capitol Hill.
Another moderate Senator, Evan Bayh (D-IN), retired prior to the 2010 Midterm elections despite having a 20 point lead over his opponent and $13 million in his "war chest." Here's a video of his retirement speech, where he addresses the collapsing middle. It's one of the saddest purely political moments I've seen, and it's haunted my thoughts of partisanship ever since.