Back in animation school, my very first Flash project was to create a web page with working linked buttons that directed to various frames. I'd slaved over my design for weeks, and the night before the due date was just checking a few things at the school lab when, while publishing a preview, the file crashed mid-publish...and corrupted, refusing to recover even an iota of the data.
Not only was my last saved iteration was over a week old, but I'd accidentally left my zip drive (yes, we still used those back then) with backups back at the student apartments and it was well after midnight, with the project due in the morning. The worst part? After bumming a ride there and back from a friend, I found out that I'd last saved an iteration of the file over a week before. I had less than eight hours to reproduce the rest. Now I could probably do that work in about twenty minutes, but back then Flash was new, shiny, and somewhat baffling.
The good news is that after much coffee and swearing I finished the project on time, and even made some improvements to the design that I'd glossed over in the first draft. But I learned a valuable lesson: save backup copies every day. Twice a day, maybe more. As much as necessary. Heck, sometimes I save an iteration after I make a major change to something, just in case I want to go back and undo it.
I could tell you more stories - like the time my Flash install corrupted the day before I had a major project due for a client, or the time I installed CS3 on a new rig and immediately had the whole rig go down (had to restore from scratch from the manufacturer's disks). But I'm more interested in you; what are your horror stories?
