Rebecca Kraemer wrote a really great post at Small Dog’s Apple blog called Backup of your Backup, on why it’s important to back up your backup. (This was part 1 of a 3-part backup article.)
It’s not a situation that occurs too often, but it can happen: Your computer hard drive and your backup drive both die at the same time. Or more frequently, some sort of corruption or virus hits your computer and then gets transmitted to your automatic backup (for example your Time Machine drive).
I’m paranoid about losing my data, so I have multiple backups going. I have a Time Machine drive attached to my computer. Then I have SugarSync which syncs my work files on my work computer to my home computer–and my home computer is also backed up using Time Machine. So now I’ve got a backup “in the cloud” (offsite) as well as in different physical locations. Last, every 6 months or so, I do a full backup to another external hard drive and put that drive in a separate location.
Is this overkill? My motto is: You can’t have too many backups. It’s worth the extra time, to be insured in the event of an emergency. Your data–your emails, your company financial data, your photos–is impossible to recreate, isn’t it?