Not a flame.. just a constructive-criticism... :-) The biggest flaw that comes to mind is that it's based purely on the honor system, as it is currently designed. While it would still be a "fun" game, you would have to work out some form of verification before it could be "serious competition". Do you have any thoughts on that yet?
A description could be faked by pulling up maps and overhead photos on Terra Server. A photo of the GPS can be faked (most receivers can go into a simulation mode).
It's a great start... very akin to a scavenger hunt. Now, if the contest coordinator has already visited those sites and knows exactly what they look like and requires a photo taken in a specific direction at each waypoint then it might be doable, especially at the local and regional levels.