I've bought some movies and cd's twice by accident, but not games. Many more on purpose though with laserdisc, dvd, blu-ray versions and directors cut of some movies :/
I have 2 copies of forza 2 due to it being packed in with my rrod replacement model.
I bought Ico a 2nd time since I was playing it when I moved from pal to ntsc territory and will get it again when the HD collection arrives.
I have braid on 360 and ps3 because the developer deserves it.
And I got some games double on steam with some multi game deals, but they let you gift the doubles to your friends :)







