Xbox360Achievements.org lists Portal 2 achievements, noting there's one in the first-person puzzle/platformer sequel called "Ship Overboard." There are user comments there and on Reddit, with lots of speculation that this is a reference to Aperture Laboratories' lost ship, The Borealis from Half-Life 2: Episode Two, and further speculation that there's some aspect of Portal 2 that ties in with Half-Life 2, and perhaps even Episode Three. Feel free to speculate as well, but as always, be prepared for unforeseen consequences (and remember the cake is a lie). Thanks nin via Joystiq.