This looks like it could be a very hackable little device: http://gearjunkie.com/garmin-chirp-gps
I personally don't have the skills required yet to hack it up to my uses, but I'm sure someone does!
It sounds like it just contains some sort of wireless transceiver and EEPROM, nothing GPS specific. The manual here doesn't say anything useful about the RF band or which territories it is legal for: http://static.garmincdn.com/pumac/Chirp_OM_EN.pdf
ISM band transceivers are a few dollars, this is simply one repackaged with a simple upload/download protocol?
At $25 a pop, it might be interesting to see if there is a low-cost hobby alternative. Reverse engineer the radio the Chrip is using and build your own for Geocaches.
Sounds like this is using Dynastream's ANT technology, which Garmin recently acquired. (http://thisisant.com). I know a guy working on an open-source PC-side client for ANT protocol (https://github.com/qdot/libfitbit/tree/master/python), but there are no Arduino libraries for it that I know of (yet) 
I might try my hand at rolling a simple library for generic ANT radios as part of an unrelated project, but it's a ways down my todo list!
Here’s mine 
It has nothing to do with Arduino, I just found this thread looking for what others have done (which is nothing).
