This is something I have seen twice now. It happened once to me on Fedora 15, and once to a co-worker on Ubuntu 11.04:
1. Copy a large amount of data to a USB stick.
2. Forget what you are doing and remove the stick while the system is writing.
3. The system then damages the hard disk rendering the machine unbootable, requiring a re-install.
I really don't think that should ever happen. There is something awfully wrong in the file system management.