Ohhh, yeah. Happened to me in a big way a couple of times.
First when I was writing my fanfic, The Price of Peace...I made it all the way through, and went back, double checking my work, only to find that I had saved Chapter 16 over the top of Chapter 18 (I had named it wrong, apparenlty). Chapter 18 was a 30 page chapter or so.
Luckily it was fresh enough in my mind, that I was able to go back and rewrite it from the ground up, and fortunately enough, I actually ended up liking the second version more. That almost killed me, though...I nearly scrapped the whole thing right there.
Second time was when I was in the middle of Power Struggle...my CD Burner crashed while I was working, so I couldn't backup any files. I had a warranty with Gateway and brought it in to the local Gateway store. They asked what files I wanted backed up, in case they wanted to wipe it out and I was VERY specific.
Of course I got the computer back wiped out WITHOUT the specified files I had wanted.
Gateway's excuse? "We don't backup .PSD files". I was like well, you coulda told me that right when I wrote it down on the friggen piece of paper I had! Plus, most of the stuff in the folders I wrote down were .jpg's anyway...
Can we tell I have some pent up frustration here?
Anyway...now I try to do very regular backups. I actually use a section on my iPod to backup my website information pretty regularly.
But, as I did with the chapter of The Price of Peace, I sucked it up and reshot what had been lost...
It's a bummer, Dan, I hope you can get it ironed out!
Justin