Like the title says. I don't know if this helps Obama much, but, if nothing else, Kerry's endorsement could come in handy in Massachusetts on February 5, where Obama already has the support of Deval Patrick.
P.S. Of course, the one endorsement from a Democratic nominee that would help is Gore's, but I recently asked a couple plugged-in Democratic politicos if they thought he'd ever pull the trigger, and they all said they doubted it. Their thinking was that, post-Nobel, Gore's almost above that sort of thing.