Inspired, I think, by Marco Arment, I trebly back up my computers:

1. To a Time Capsule at home.
2. Via SuperDuper to an external hard drive that sits at work. (I couldn’t really tell you how this differs from just using dd(1), other than that it has a nice UI, only copies the diffs, and seemingly makes the external disk bootable. In any case, it’s great.)
3. In the cloud to Backblaze.

I have my laptop set to automatically back up to the cloud at all times, and my girlfriend’s laptop set to do the same. Then I use the Backblaze iPhone app to periodically ensure that all my backups are up to date. It’s awesome. The best backup is the one you never have to think about, and I definitely don’t have to think about this one.

…and if you decide to use Backblaze, too, I can get a cut. It’s great. I would never recommend a product I didn’t use enthusiastically, and I wholeheartedly recommend Backblaze.

(As it happens, I also wholeheartedly recommend my Time Capsule and SuperDuper, but they offer me no way to get filthy rich, like Backblaze does.)