It seemed a little strange that the ultimate co-op game, Portal 2, supported split-screen co-op on its console versions, but not for its PC version in Steam's Big Picture mode.
Fortunately, Valve's seen fit to correct that oversight. Now, when playing Portal 2 in Big Picture mode, plugging in two controllers to the PC running the game and then hitting 'X' on the first player controller's co-op menu activates local co-op.
The update also tweaked a few issues with Portal 2 in Big Picture mode. Players will now be able to exit the Robot Enrichment or Create Test Chambers menu with a controller and the quick ping issue, which froze movement, should no longer be a problem.