"The challenge is to be the first to submit the locations of ten moored, 8 foot, red weather balloons located at ten fixed locations in the continental United States. Balloons will be in readily accessible locations and visible from nearby roadways.
A $40,000 cash prize will be awarded to the first entrant to submit the latitude and longitude of all ten balloons."
The fastest method I could imagine would be to write a computer program that would search for red blobs on Google Earth or other mapping sites, and get a bunch of people to search through the thousand photos the program flagged.
But DARPA suggests that this is a social networking challenge. Maybe there's a quicker way to do it by crawling people's websites looking for "red balloon", as people randomly see the balloons and mention them in their blogs, LJ posts, facebook posts, etc.