For those of you that are not aware, in March of 2010, valve engaged in an alternate reality game, involving sneakily inserted data and clever codes, ultimately resulting in the announcement of Portal 2. Information on the original ARG can be found here: http://half-life.wikia.com/wiki/ARG
Now, it's happening again. On April 1st, many games, including cogs, amnesia: the dark descent, audiosurf, bit.trip beat, killing floor, and super meat boy were updated with cryptic patch notes that all contained the phrase "happy #potatofoolsday". Many of these games had, in these updates, potato references (super meat boy becoming super potato boy, potatoes on the title screen of bit trip, etc.) Most people brushed this off as a collective April fools joke. however, the potato references persisted after April fools day. Since then, many cryptic clues have come to light, including strange, jumbled sentences, strange glyphs appearing in textures, and new levels being inserted. The game ahs since become far too complex to documant in a single forum post, so I'll link you to the wiki instead: http://valvearg.com/wiki/Valve_ARG_Wiki
This is all the information the community has gathered on the subject thus far, and the evidence is pointing towards something related to portal. Take a look around and help out if you can. We can't have too much help.