The news that Sen. Evan Bayh is retiring is generally good news for the progressive cause. Bayh supported every war Bush got America into, supported every tax cut Bush proposed, and has steadfastly opposed meaningful health care and financial reform. I'm not sure how Bayh is actually a Democrat, but he's pretended to be one throughout his career, and has done immense damage to progressive causes.
However, as Bob Cesca points out, Bayh "mostly votes with the Democratic caucus is the best we can hope for (for now) in states like Indiana." The prospect of a Republican taking his place is truly horrific, and to that extent, a centrist like Bayh did serve a purpose.
But then again, there is still the possibility that a more liberal candidate could take his place should the progressive community spring into action and help fund one. They have until November to do it, so let's hope they make Indiana a battleground for the progressive cause.