I was doing a similar concept last year with 'Landmarks' but passed my project off due to grad school (I wonder what happened to the geocaching guys?) I really do wish they put more time into this before attempting to launch, as the concept could have been awesome,  both as a fun way to use coins for smartphones and as a successful business model.   It just seems half-put-together.

I will still use this if I can,  just make sure to make it fun and spend a decent amount of time establishing physical faucets at interesting places and landmarks.