Don't be an idiot!

[cd34]

Raid doesn't prevent accidental deletion of a directory tree.
Raid doesn't help if your machine is stolen or burns in a fire.
Raid doesn't help if you get a virus that overwrites your MBR. Raid will faithfully write those changes to the mirror.

Don't get me wrong, Raid is good, but, its still no substitute for making backups, preferably off-site backups.

And I couldn't get Raid-1 working in my laptop -- so, nightly, my laptop is backed up to a storage server that maintains 5 generations on raid. And those are backed up to a disk that goes in the safe on a monthly basis. Recently, I've decided that another backup needs to be maintained at the local bank.