Chief, RAID is good for uptime (ie. if one drive fails then the system continues). But it doesn't replace backups. If you muck up your system by accident, or a virus does so, or whatever...a backup will save your butt. RAID will just make sure you have two copies of it
Plus when a drive fails, you have to go out and get a new drive and install it and rebuild the RAID...and what if something happens during that time?