Apparently Robin Williams popped up out of the audience at a TED session to entertain everyone during a technical glitch. From what I here the best joke was a Google one:

He didn't spare panelist Brin and Google, noting that if you walk into Google you see everyone in front of their computer sitting on exercise balls, "which I think is how they're hatching new employees."

I love TED and I'll be trying to post interesting stuff from it once I have time to go through the videos and stuff.