Didrik Johnck's Weblog: Saved by a CD:

An object lesson - backups are important, folks.

Really important.

What's the lesson here?? A single electronic backup is not enough; always do a third backup on some type of permanent media like a CD or DVD.

That's where it gets really complex - CDs and DVD aren't permanent either. They degrade over time. Some faster than others.

My current personal backup strategy, involves copies on a mirrored drive on a local server, as well as copies to DVD, and electronically off-sited copies on another server, in another part of the world. And I'm still paranoid about something happening to all three sets at once.