Jonathan Blow, the guy who created the game, has revealed there are still 2 minor bugs left in the game. The bugs are a bit too specific to fully explain, suffice it to say that if they hit you it's going to mean a fair amount of backtracking. They don't seem to be especially common, but they're serious for those who've been afflicted. The good news? While Jonathan Blow is spilling the beans, he's also working with Microsoft on solutions.