I have learned through recent debacles. :}
I back stuff up on line.
I back it up on both the always-plugged-in external drive, and on an external drive that is plugged in once a week, loaded, and then removed.
So that's three ways - AND I email stuff to myself, as well, (and have recently been able to recover something from Google Documents, as I'd used that to prepare something for going online elsewhere).
Add to that - backing a lot of stuff up onto disk.
So - belt, braces and something else.
Am I the only one this paranoid?
Well, I felt very silly to be caught out, when I so constantly tell students, etc., that "if you don't back it up, you don't care about it" - and
then I had data loss!
Not much and not catastrophic but still - silly of me. :}
I back up to a second HDD fairly often, and to another PC almost as often. I burn to DVD also. I had a situation recently where all of my computers were "seized" by the constabulary (unproven allegations that were shown to be unfounded) I was up and running again within 24 hours with minimal loss of data. it took them two months to return my boxes so it was a nuisance, but that was all. The only critical data was related to the wedding which had not been backed up off-line locally, but that daughter had, that was a pain in the proverbial!