This is the best overview that I've run across for describing all the different RAID versions.
AC&NC - RAID.edu - RAID Tutorial & Benchmarking Tools
And Rekna & Martain are right... RAID just keeps you up during a drive failure. There is still a need for off site backups if you are working on an enterprise level. As was stated... if the building burns down... no RAID or on site backup will save you.
Oh... and for what it's worth... I run RAID 0 on my main PCs to boost performance. They are backed up weekly to my home server which runs RAID 1. I used to run RAID 5... but with Terra byte HDs now being so cheap I fell it is a waste for my home application. The house server also runs a weekly backup to an external HD that I can take with me to friends and family's houses to share larger files than what are conveniently hosted through my FTP site.
Since my parents don't have a home server, I've set their PC up on RAID 5 to give them a boost in speed along with some HD failure insurance (which paid off about a week ago).
One of my friends (who also lacks a home server) felt the need to set up his home PC on RAID 6, although I'm not sure that it has ever paid off for him.