A friend of mine has spent the past few years working on a platformer that randomly generates levels, based on various settings you choose, and scales difficulty based on how well you've been doing at the game. He's pitching it to Microsoft next week.
http://www.rockpapershotgun.com/2012/02/07/not-mushroom-to-maneuver-cloudberry-kingdom/
http://www.rockpapershotgun.com/2012/02/07/not-mushroom-to-maneuver-cloudberry-kingdom/