We sort of sat on this one despite all the rumours about it, due to a combination of thinking it was an April Fool's thing, our usual elderly-style bewilderment and being distracted by my cat chasing a bit of... Oh! Look at her! It's adorable! She's rolled over now! And she's purring! And..
Oops, I did it again. Oh yes, the Valve ARG. This is elaborate and packed with delectable mysteries - but what does it mean?
Assorted clues and hints were stuffed into the recent Potato Sack sale shenanigans - specifically, hidden messages (and potatoes!) in some of the games featured in the pack.
There were strange crossovers too, such as glyphs found when playing Super Meat Boy music in Audiosurf. Later still, Clever Internet Men discovered clues in real-life locations too. The glyphs are still being collected, and hopefully Important Truths will be revealed once they're all located. Here's a chap discovering one of the glyphs outside the Dutch offices of Toki Tori devs Two Tribes:
Which is, I admit, sort of useless if you've not followed the tale to date, but hey: ducks! Potatoes! Tacos!
So I can give you no answers for. The story's still evolving, with little sense of where it may ultimately be going, but it appears the most recent Portal 2 video may be in on the act too. For full (frighteningly extensive) details of the story so far, get thee to the Valve ARG Wiki. Those chaps have found a whole lot of things. Too much. They should probably be killed; it's the only way to be sure. Alternatively, see if you can help them out. MOBILISE.
Oh, and apparently the number 16 may be important. THEORISE.