The idea is that if an iPod is stolen and then later attached to an “unauthorized” PC, the device will recognize the machine as such and then disable its ability to charge – forever. It does this through the use of an intelligent circuit that can prevent charging if it fails to find a proper security code on “authorized” machines.
What exactly qualifies a machine as “authorized” isn't mentioned, nor if the device would be able to be unlocked if it was later recovered by the proper owner... or what would happen if the “authorized” machine needed an OS reinstall. Still, the concept is interesting. You can read the patent filing for the tech.