By who? All the big market teams that would normally be a threat are either cash strapped, rebuilding, or have a guy. And the market is going to be saturated with quality high end RP arms, meaning that the highest-end guy is going to have to compete with "better values," which wouldn't matter so much for SP or position players, but we're talking about a relief pitcher here.
The Yankees aren't going bring in someone that high-profile behind Rivera, they'd have a riot on their hands, they're stuck with that situation for at least 1 more year, and probably most of 'em don't mind one bit. They'll probably bring in a guy like Valverde instead who's not a threat to Mo if both are helpful but is a viable replacement.
So who's really going to compete with the Sox for Papelbon? The Tigers are the only team out there that's in position to make a move, and they're not big "elite closer" type of team. I have them pegged as Dotel's next team. They're gonna look for a quality pitcher to replace Valverde, but they're not gonna bust the bank on a reliever, it wouldn't be like that GM. The rest of the teams that have the open role and the cash aren't contenders, I can't see Papelbon taking them seriously (teams like the Jays, O's, White Sox, Mariners, etc.)