I'm guessing that nastiness per se plays to Hillary's advantage--this is where Obama could face questions about his "new politics." But it depends a lot on who gets in the better shot. (Update: An Obama-boosting friend emails: "Ordinarily I would agree, but I think Obama needs to show he can fight hard, otherwise people will worry about McCain or Romney chewing him to bits.")
Meanwhile John Edwards gets a fine chance to rise above the fray. A couple of months late, probably.