I don't actually use a back up system. What I've done is transfer my work over to a new machine whenever I get one. The older machines are wiped / sold. At the moment I have a mac book, if I lost all my work I'd start something new. I'd be gutted, but I'd start something new.
christian, has you ever thought of getting a second email, then emailing your work in progress and your back up files to yourself..? the bonus being that as well as a back up, if you are at a random computer you can open the email and work for a bit on your chapters, and then send it to yourself... i do that with pictures on vacation, that way if my things get stolen then i lose very little.