Story here. Although I haven't confirmed this with Professor Sisk, my guess is that had Sunstein been included in the recent scholarly impact survey for Harvard, Harvard would have been #1.
(Thanks to Eric Freedman for the pointer.)
UPDATE: Professor Sisk informs me that even with Sunstein, Harvard would still trail Yale in citations, though by a much smaller margin. This may be a case where mean/median citation figures are misleading, since it seems to me (and I imagine others) that Harvard overtook Yale some time ago.