Anyway, my roommate David also got an iPhone, and has been busy playing with the GPS on it like...well, I don't really have a metaphor. Like a guy who's having a lot of fun with a GPS gadget, I suppose.
The iPhone is now open to third-party developers, and the Cocoa API has been extended dramatically with all sorts of calls related to power management, Bluetooth, and GPS functionality. In other words, the GPS system is exposed to third-party developers.
David, who actually isn't a perv, came up with an interesting idea, that he calls the "Virtual Leash." His conception is of a sex toy like a vibrator, preferably Bluetooth-enabled (though I suppose USB would work as well), designed to be locked into place in one's girlfriend. The device would be controlled by software on the iPhone that would monitor the wearer's position via GPS, so that if she left some pre-determined area, the vibrator would start running. At full speed. And not stop until she returned to that area.
Neither my mad Bluetooth hacking skillz nor my iPhone development skillz are up to tackling this project, but I know several folks on my flist could probably make it work. Any takers?