I always miss my bus in the morning. I've had the idea to stuff a remote tracker in one of the bus seats for a while... this makes it possible.
It is dependent on independently operated base stations to relay data to the internet, and since all transmitters contend for the same frequency it may not be feasible in high-use areas. You also need a Ham technician license (35-question written exam).
On the plus side, it's totally free to use.
Wiki on APRS: http://en.wikipedia.org/wiki/Automatic_Packet_Reporting_Syst...
Live feed of beacons in the SF Bay Area: http://aprs.fi/#!lat=37.87810&lng=-122.27100