I'm jumping the gun here, since they haven't even announced the dates yet. (WTH, Smash? WE'RE TWO WEEKS INTO THE NEW YEAR ALREADY.) But I think we can assume it's July 25-27.
Outkast (announced 40 summer gigs)
Neutral Milk Hotel
Pains of Being Pure at Heart
Since Summer Sonic already announced Arctic Monkeys, Robert Plant, Avenged Sevenfold and Phoenix, we won't be getting those.