Now we know: Portal 2 will launch early—if enough people get together and play all the indie games in the "Potato Sack" on Steam. The countdown clock ended a noon, revealing the "GLaDOS@Home distributed computational grid status" page, showing what appear to be real-time stats of how many people are playing the games of the Potato Sack, as well as a projected time to unlock Portal 2, which at the time of this writing is showing just shy of 94 hours.
That's not nearly fast enough. To the gaming PCs! Be fleet and enjoy one of the thirteen games, which include some real gems like Defense Grid, Bit Trip Beat, and Super Meat Boy. The more people that play the games simultaneously the faster the clock will count down. (We can only suppose!)