Most annoying times when you've had save data erased/go corrupt?

[Gilgamesh]

Try loosing a Final Fantasy VII save when I was about 3 quarters done of the game, twice! (this was before I ever beat the game)

I lost about 20 hours of gameplay on one of my oblivion saves.

I lost about 15 hours on one of my fallout 3 saves.

I lost about 40 hours of gameplay in GTAIV.

And never expect to have a game actually save and still be there on a SNES I learnt my lesson quick.