Madonna’s "thank you" performance at Roseland last night brought out all sorts of fans and all sorts of celebrities, including Gossip Girl’s Michelle Trachtenberg and SNL vet Chris Kattan!  We spotted the two leaving the concert last night, I’m only presuming they didn’t show up together, that’d be waaay too weird!  But who knows, now that Amber Tamblyn and David Cross are an item (ew) maybe this young ingenue/old dude pairing is new fad!