Game Informer speculates that this could be the first Portal 2 DLC release thanks to the memo mentioning "Pneumatic Diversity Tubes". These tubes were shown in videos for Valve's puzzle shooter sequel in 2010 when the game was first announced but for some reason didn't make it into the final build of the game. Will this be the first of many DLC releases? Stay tuned.
Update: Looks like whatever the update is will have to wait; the site is currently down.
Update 2: False alarm: It's just the creators of the Valve ARG Wiki thanking Valve and the game developers of The Potato Pack for their role in the Portal 2 ARG.
Gallery: Portal 2 Screenshots