Lets see, for Final Fantasy X my cousin got his hands on my memory card and deleted my save files, forcing me to start from the beginning. Due to starting it and then having a year break I had to start again on Star Ocean 3. Its mainly RPG's that it's happened on really, since the story often doesnt matter I wouldnt need to start again if I forgot it, plus since usually theyre short, it doesn't matter as much starting again.
Oh yeah and I'm on that boat with the xbox games, dead gutted about Morrowind, and Jet Set Radio Future. SHenmue 2 I didnt mind starting again since it was so awesome.
Oh yeah Pokemon too, my cartridge battery went, so my long hours spent on the game was lost, including all my epic pokemon which were all at lvl 80-100... >.< Replaced the battery in it now so I could continue playing, my save is still lost though. =/