I divide backing up data into several levels:
Level 0: No backup
Level 1: Backup
Level 2: Redundant back ups (Save As instead of Save)
Level 3: Offsite backups
Level 4: Testing backups
Most guides will tell you to get to level 3, but I don't think I've actually seen any that tell you to test your backups. This seems pretty important though - you don't want to need your backup only to find there's something wrong.