Portal 2's PC release is tied to the Steam game store and distribution platform, and that platform has been pre-loading the game's assets for those who have preordered it for a little while now. Given that the release date is a matter of one final patch or key being released to the target systems to unlock the mass of binary data just waiting to spring to virtual life, Valve decided to turn their marketing up a few notches and have some fun along the way.
The release date for Portal 2 has been given a community co-op twist. The more time spent actively playing one or more of a collection of indie titles available on steam called the Potato Sack games, the greater the chance of moving up the release date for the game and unlocking it early. An Aperture Science page named glados@home charts the progress thus far.