I am also interested. I had just moved to a mac from a pc. I always ran 2 separate backups independently in case one failed, or was stolen. It is not to be at a remote location or off site, just well hidden!!
I still think that the idea of a separate backup is a good idea. I don't like the idea of backing up the Time Capsule directly, though. With the Time Capsule, each Mac's backup is contained in a file called a sparse image, which can become corrupted. If this file does become corrupted on the Time Capsule, and your separate backup consists simply of backing up what's on the Time Capsule, if you're not paying attention you may end up with two copies of a backup that is corrupt.
IIRC, starting with Mac OS 10.8, the Time Machine feature on a Mac officially supports multiple backup devices. So 24/7 (as long as I'm home), my Macbook Air backups wirelessly to my Time Capsule. For my separate backup, I have a cheap portable USB 3 external that I leave at my desk at work. Since this is an external drive (vs. a wirelessly attached Time Capsule), backups don't use a sparse image. Once a month, I bring it home, plug it in, and Time Machine will automatically update it. Then I take it back to work. I set Time Machine to encrypt these backups, so if anyone at work snags the drive, they won't be able to see anything. Makes me feel a little better know if anything big happens at home (i.e. house burns down), a month of data is the max I will have lost.