Valve's Portal Puzzle So Far on Kotaku
I love viral marketing when it's done right.
Kind of reminds me of that attempt at a live-action immersion conspiracy game EA tried 10 plus years ago called Majestic. You could get phone calls with recorded messages at any time of the day and clues you'd have to research yourself online to piece together what your next step would be in the game. Ambitious, but it ultimately failed.