OK - I'm a bit of a belt, braces and another belt type of guy.
Primary backup is an online system from a company that we are channel partners for. This backs up almost all of my personal and company data (some exceptions, listed below)
Everything in "My documents" (which includes all my company stuff, MP3s and videos) is synchronised to a laptop (strictly speaking - not a backup but a copy as I can only get back the latest version).
MP3s, videos and photos are synchronised to an NAS device (again, strictly speaking not a backup)
MP3s & videos that haven't come from CDs or DVDs (e.g. downloads, own recordings, etc.) & photos are copied onto 2 DVDs, one onsite, one offsite. There are 2 sets of DVDs so that I never overwrite the latest backup
Finally, ex-clients are archived to 3 DVDs, 1 onsite, 2 offsite.
As for disasters - several, fortunately none mine. I've had disk failures, but my backups have always worked. I've had clients phone saying their disk has died and can I recover the data - usually the answer is yes, but the cost is as much as they would have paid for 5 years worth of backup, and it takes longer to do the recovery.