If I have problems with my startup drive, or with Mac OS X, I can instantly boot from that volume and try and solve things. Even though I don’t run these clones daily, I have my other backups of user files on another partition on this backup drive, and can access my Time Machine backups at any time. I needed this a few months ago, when, suddenly, my Mac froze, and I couldn’t reboot. All the data seemed fine, but the startup volume was no longer “blessed,” meaning that Mac OS X didn’t see it as a valid system disk. I booted off the clone, copied over my Users folder, then cloned the clone to the original startup volume and rebooted. This too an hour or so, but much less than a full restoration with Time Machine would have taken.

I’m not a big believer in “the cloud” for backups, because of the time it takes to send data to a server. My outgoing bandwidth is only 100Kps, so large backups take hours. Nevertheless, since I have a account, I use Apple’s to run an incremental backup of my home folder to MobileMe once a week. I’ve never needed to recover any files from it, but who knows? I may need it some day.

Just in case you thought the above was obsessive enough, there’s one more link in my backup chain. While a lot of people suggest off-site backups, it’s not really practical for me: I work out of my home, and I can’t store a backup, say, at my office. So I have a fireproof safe in my basement, in which I store backup disks.