I can’t say enough about how important it is to occasionally backup your data. I’ve had several instances where doing this really saved me, and I’ve had friends who didn’t do it, and it has really cost them. I’m a firm believer in the awesomeness of Time Machine on the Mac. I’ve used it a few times to restore my system to a previous state, after I thought my system had been compromised, and it’s just a thing of beauty…for the most part.