Lots of people don't backup their data enough...then complain when it is lost. This will happen - it's just a matter of time until it happens to you..!
I use lots of small CF cards, a backup to my home network, a backup in the firesafe and a backup on DVD at my brothers house just to be sure! I was burgled and had my computer gear stolen hence the paranoia!
Then there is fire risk, flood risk or an asteroid may land on your house so make sure you have an offsite backup as well!
And make sure the backups work! Read a sample of data back to make sure they do...