I managed to lose four to six hours of writing a couple of days ago, apparently by being a klutz. I hadn't saved, figuring I had autosave set for every ten minutes. As near as I can figure, I accidentally hit some keyboard combo that meant close this file, then did something that the computer took as "Don't save changes." Zap. Everything since the last save = gone. The autosave file apparently disappears when the file is closed. I tried an undelete program, but it couldn't find the autosave file. It probably got written over by Firefox's voracious cache. Moral of story: Save often.