Backup is SOOO under-appreciated – people just don’t realize how important it is until AFTER it’s too late. Good for you for bringing it up (again.)
I started my current backup plan on accident – my laptop ran out of harddrive space, so I bought a 750gb passport drive and moved all my data to the external. Shortly thereafter, Mozy got rid of their unlimited plan and my backups were about to skyrocket in price, so I bought 2 more externals.
Today I keep one external drive plugged into my office computer full-time, and I travel another one back & forth in my briefcase. I use Allway Sync to keep them completely sync’d. (along with making sure anything on my office harddrive gets sync’d to one, and then the other, external.
Then, once a month, I bring the 3rd external to my office instead of the one that normally travels, and I sync that with the one permanently at my office computer.
Now I have 3 drives, all in sync, and never in the same location at the same time. And since my office is 20 miles from my house (and I’m not in a densely populated city), it would take an awfully big disaster for me to lose all 3 drives at once – I’m ok with those odds and sleep well at night. :)