I'm glad you broached this subject.
I think it's wise to back up as often as you can.
How often to internal non-boot drives and external boot drives go bad?
"C" is my boot drive. I save all my files to my "D" drive. I periodically back them up to a external drive.
I've had boot drives go bad but never an auxillary drive.
When my boot drive goes bad all I lose is email and my email settings (such as sending emails from certain senders to specific folders rather than my inbox). Is there any simply way to get around this? (I back up my address book periodically so that's not an issue).
Now to put Lil B's claims of being anal to shame...

I'm strongly considering burning files to DVD and storing them at relative's homes in case of fire, theft or natural disaster. I'm also going through and our scanning all our pre-digital camera photos for the same reason.