1. I did not know I was not supposed to change the orientation of the 360, that left a really nasty scratched out ring about halfway down the radius of the disc (Oblivion). I was never able to buff the scratch out, even with a buffing machine. I always RTFM, and I don't remember a warning on changing the orientation of the console while a disc was inside. I ended up burning my surplus points in Goozex.com to get a replacement disc.
2. I left a disc inside of the Xbox while the house was being fumigated. The poison seeped into the Xbox and somehow the disk soaked it in and the surface became cloudy. No scratches, the surface remained smooth, but it looked pretty fogged. I don't see how I can blame Microsoft for this one, I should had just shut everything down before I left the house.