I was there tonight too! I noticed all the giggling at the end of the show too. It seemed liked when they all went upstage before the final moments, maybe someone said something to them all...and when they went into their whole "in the future" bits, they were all looking down and giggling hysterically.
Oh, and the line about the girl dressing up "going to a spelling bee and not a broadway show" totally cracked me up!
"Hey little girls, look at all the men in shiny shirts and no wives!" - Jackie Hoffman, Xanadu, 19 Feb 2008