Completely indepdendent of what one thinks of Lieberman, it seems obvious to me that a primary campaign would be dead in the water. I think Josh Marshall's comparison of him to Phil Gramm is apt.
UPDATE: You know, Josh Marshall doesn't actually compare Lieberman to Gramm. *SOMEONE* did recently, or maybe I dreamt it, or maybe I had a bit too much to drink last night and then woke up too early this morning and...oh who the hell knows where I got that.
UPDATE 2: It was Gene Lyons.