I got a Japanese 2GB Sony Pro Duo stick with my PSP when I got it off ebay. It was fine for about two weeks and then all of a sudden both my PSP and USB memory card reader failed to recognise it. The PSP seemed to think there was no memory card inserted. Luckily the seller is a legitimate UK seller with their own buisiness and has agreed to exchange it. I just hope the same thing doesn't happen again. I can't think of anything I could have done to damage it, I didn't yank it out whilst it was reading/writing or anything daft like that.