is often something that people do in response to an earlier disaster. Regular forum users will be tired of me repeating this, but there's an old IT-industry joke that the best time to back up your files is just before your computer crashes.
It's not unknown for CDs to shatter in the drive, and it makes good sense to double-up on the backup copies. In the corporate world backups are commonly made to tape drives, and I always advise clients to remove at least one backup copy from the premises each night - usually a responsible member of staff is nominated to take the backup home.
In the home-user situation there's less need for such stringent routines, and a couple of separate CD or DVD copies would seem appropriate. I'm not generally in favour or retaining critical backups on hard drives for obvious reasons - far better to keep backups on some kind of removeable media - although disk imaging is a different matter. I'm referring to data backups.