Portal 2's totally free DLC "Peer Review" is now available on Steam as well as Xbox Live and the PlayStation Network. Excitingly, the DLC delivers a brand new co-op track! If you don't yet own Portal 2, or Portal for that matter, they're dirt cheap on Steam right now. The official word from Valve with the specifics is as follows. "If you notice Portal 2 updating today, don't be alarmed: it's only because you're getting the new Portal 2: Peer Review DLC for free. If you don't have a copy of Por...