TechnoMonkey,
RAID is not a backup. It is for fault tolerance.
RAID is used to protect data from drive and system failure, but think of it like this: If all your data was on RAID boxes, and all those boxes were in one room, and the room burned to the ground, did you have a good backup? An other example is a RAID mirror. Deleting something off one mirror, removes it from the other mirror. That isn't backup either, it is just for fault tolerance.
Yes, I keep my backups on RAID, but it isn't a good backup strategy, it's a fault tolerance strategy to keep things running in the event of failures. That might sound semantic, but you can do much more reading about it from Lloyd Chambers
here. Or read his entire RAID info
here. It's fantastic reading.
dfw