they applauded during the movie marathon of all three, but not once, which would've been acceptable. they applauded at the beginning of the fellowship of the ring, then when aragorn chops of the orc's head at the end--that was more of a cheer, actually--and then at the end of the film again. they clapped at the beginning and end of the two towers, and they clapped at the beginning and end of return of the king.
it was a lot of clapping.
it was also really pointless, but hey, whatever makes people happy, right?