Been on the receiving end of a few such calls.
One was someone ringing the support line to say their database wasn't up. I asked them to check the database directory - it was empty. They had seen the disk was a bit full, saw some large files, and did an rm -rf. Poor lady was almost crying down the phone - no backups for 4 days.
The other was someone who managed to do an rm -rf from '/' but not as root. Not that it matters, because that can bork a machine just as much as completely deleting everything. Worse still, he did it twice! The first time we left the server (Linux) still running - we didn't dare turn it off or reboot it until we could work out what we were going to do. The second time.... :)
Biting the hand that feeds IT
