Jeep Barnett, a programmer with Valve, has given an interview with Gamerzines. In that chat (which is well worth a read), he has let slip a little more about how Steamworks will be integrated into the PlayStation 3 version of Portal 2.
It seems that players will need to have a Steamworks account in order to use the co-op functionality on PS3. Your regular PSN account will not be enough.
You have to create a Steam account, which again can be via that quick create where all you’re doing is clicking a button saying ‘hey, I wanna play’.
Don’t worry though, that doesn’t mean that Valve are cramming annoying DRM into the system. Jeep confirms that although the boxed-in code that gives you ownership of the PC version (via full Steam account download and only with the PS3 copy of the game) is only redeemable once, you don’t need that code to use the PS3’s multiplayer functionality.
You don’t need to input the code. You don’t even need to have a full Steam account.
So you only need a quick Steamworks account to play PS3 co-op but the code in the box allows you to link your PSN and full Steam accounts in order to download the PC version of the game for free.