Apple co-founder Steve Wozniak drops stealth: wireless tracking in 900 MHz, ubiquitously (free reg. required): Woz's company, Wheels of Zeus (WOZ, get it?) has a device that can opportunistically use any local network operating in its format to report on GPS-identified whereabouts of people, animals, and things. WOZ uses the 900 MHz unlicensed band, and operates at about 20 Kbps.
Interestingly, many of the location-based Wi-Fi systems use the flip side of this: they figure that range is small so if you identify the location of the access point, you can triangulate on a user and pinpoint their location. WozNet identifies the location of each low-speed, long-range (1 to 2 mile) device, liberating the access points.
It's not too far in the future that GPS becomes a necessity for travelers and affordably built in. This is yet another example of its utility.