Death by Delete - Backups, backups and test your backups
"One day, a developer was optimizing the database and removing records that MegaPetCo no longer needed. All it took was a single, poorly formed delete query to wipe out each and every row in the database table."
"... but that was the least of the company's worries. The status of its backups was bleaker still: None. Zip. Zilch. Nada."
Death by Delete