Republicans' hearts are all aflutter at the "remote possibility" that Lieberman would switch parties. The factor that Lieberman has to be aware of, though, is that there are very good reasons to think that the Democrats are going to pick up Senatorial seats in 2008. At a minimum, of the 33 seats coming up for election, 21 are currently held by Republicans. Even if most of those seats are safe today - and I think they are - even a hawk like Lieberman must understand that if the war in Iraq is still going on in 2008, Republicans are going to be very unpopular indeed. And, of course, if Lieberman doesn't want the war to continue, there's not much reason for him to switch in the first place.
So it's not clear to me that it makes much political sense for Lieberman to actually make the jump. It's probably still helpful for him to make a fuss about the war and threaten to change parties, but it's got to be a bluff, right?
Update: Via Matthew Yglesias, apparently Lieberman becoming a Republican wouldn't change which party controls the Senate. If that's the case, then Lieberman's switching is all the more improbable.