Valve's Potato Fool's Day alternate-reality game (ARG) has taken off since we last mentioned it here. There's a history of the findings right here, which you should check out. As always, it's impressive to see all of the pieces come together, person by person.
The ARG has resulted in a considerable amount concept art for Portal 2. Super Punch has been pretty good about collecting the images: there are variations of Chell, the robots, and the game's cover art; a relaxation vault; and even a bathysphere, to get you started.
Is it April 19th yet? No? Goes back to sleep.