I also went that route for two reasons. A dedicated NAS box such as the ReadyNas Duo not only uses less power than an old PC, but also takes up much less space. This is an important point for me, as I live in central Tokyo (read: tiny apartment).

Yep, second the ReadyNas. I bought a diskless Duo (available here in Japan), and threw two 1TB WD Greenpower drives (quiet and power-saving; though spin-down isn't supported yet due to some bug apparently attributed to Western Digital). If this one starts to fill up, I'll go for the NV+ in a heartbeat.

Generally, I keep all my archived files in a folder on the NAS (it's set up with Infrant's RAID-X, which is roughly equivalent to RAID-5 with expandability), which provides me with a decent level of redundancy. My main machine is backed up on a separate external drive. Honestly, my files aren't important enough to pay for some offsite storage, but keeping the archived files bundled with my active files ensures their integrity and allows me to access them whenever.

I'm guessing this will only be useful for certain types of users. There are two real theft goals: either the thief is after the computer or after the data. I don't have the numbers, but I suspect the thief is after the computer (to sell on eBay, etc.) 95%+ of the time. Assuming this does actually make the computer inoperable, the thief will simply throw it out when it stops working (you won't get your computer/data back, and he doesn't care what was on the disk). If the thief needed to retrieve data from a laptop, the first thing an intelligent thief (say, a competitor company) would do is take out the hard disk without turning the stolen machine on and put it in a separate machine. This kind of defeats the purpose of a remote lockdown, because as far as I can tell, it requires that the notebook must be powered on. It may or may not be encrypted, but most people don't use full-disk encryption, so they get what they're after. So, this might offer a slightly higher degree of security against the first type of criminal, who is primarily after the laptop, but not the second, who is after the data (which is presumably much more valuable).