I hear you Snowleopard, I almost lost an entire manuscript. Well 80%, because my computer crashed and I hadn't backed it up since like 20k words.
I'd just plain forgotten and when I tried to go and get some of the files I'd saved on yahoo that were like 60% through the book, the mail program kept having an error, said it was a bad file type for them. I was just about at wits end until I managed to get my hard drive hooked up to something other than my dead lap top and retrieved the file.
The relief was palpable. So yeah it doesn't matter why, just save your work! I was in a funk for days until the IT guys finally managed to get me back that file. Months worth of work, yeeee
The Deposed King