He specifically mentions "changes" coming to the game (in a patch apparently "just a few weeks away") that will deal with the problem of exploits, specifically point and personal rating selling. He also says that the Arena game puts class balance "under a microscope," and says that the Lifebloom and Ice Block changes were specifically aimed towards balancing Arena teams -- Blizzard made those changes hoping that they didn't mess with PvE gameplay as much. Arena tournament players, he says, will be the "mad scientists" of class balance, so Blizzard can see firsthand what works and what doesn't. Finally, he mentions actual arena design, and reveals that in Wrath of the Lich King, there will definitely be some new Arena environments to play in.
Lots of good information in this one, especially for Arena players. We'll have to wait and see what that patch "a few weeks away" does for us, and we'll also have to watch and see what comes out of the Arena tournament -- lots of the changes that eventually show up in Wrath might come as a direct result of what happens in the tournament.