If you're a writer, you need to back up your work. We all know this, but we don't necessarily do it. I did it, but didn't back up at a separate site, thinking that the greatest likelihood was that I'd lose or damage my laptop outside the home. Instead, our home was burgled the night before Thanksgiving, and both computers - along with my backups - stolen.
I'm very fortunate, in fact. I've discussed how important critique is to my writing process, and as a result of that, I have sent relatively recent drafts of all my work to friends, who are now sending them back to me. I've only lost my most recent work, about two and a half chapters.
Needless to say, however, I'll be changing my backup strategy. There are services now which provide off-site storage for files, and even services that provide automatic back-up saves for you. A number of my friends have recommended Mobileme, or the Dropbox service, to me, so I'll be looking into them.
My message for you for today is this: however you do it, do it and don't wait. If you feel cautious about using an outside service, burn yourself a disc today with all your files on it, and then take the time to do your research. Or find a friend with whom you can exchange files regularly so there's always an extra copy out there somewhere.
I'm going off now to work on reconstructing what I've lost. Thank goodness that's as little as it is.