Ghostcrawler, a.k.a Greg Street, is the lead game systems designer for WoW. Basically that's designing the classes and other systems in the game.
He handled the crowed very well. He probably could do some stand up with his wit. When people booed about something they didn't like he'd make a joke and have them laughing the very next second. Perhaps the best moment is when he jokingly said to a question about retribution paladins: "Don't nerf me, bro!"
If Blizzard wanted to make an impression that they're listening to their fans, they most certainly did with not only having him moderate a great discussion on the beta forums for the past several months, but also please the crowd during a great class panel.
Kudos to him, and the people at Blizzard for allowing him, to casually and honestly interact with the fans.