For those of you slow on the draw, Valve has kicked off an alternate reality game to promote Portal 2, which your favorite Valve employee and mine is said to be at the helm of.
After having lurked here for a considerable time, I can say that if any community is suited to solve such a puzzle, it's this one.
A general overview of what has been found so far can be found here:
http://half-life.wikia.com/wiki/Portal_ARGA more comprehensive but less organized menagerie of information can be found here:
http://portalwiki.net/index.php