The DARPA Network Challenge offered a prize of $40,000 to the person or group who first identified all the locations.
The MIT Group which won the challenge used a clever pyramid incentive scheme. Each balloon was worth $4000. The person to identify the location earned $2000. The person who invited that person to join the MIT group got $1000, the person who invited the person who invited the person who located the balloon got $500 and so forth (any money not distributed in this way was given to charity.)
The incentive scheme meant that contestants not only had an incentive to find balloons they had an incentive to find someone who could find balloons (or find someone who could find someone who could find balloons and so forth).
Incredibly, the MIT team located all ten balloons in just under 9 hours! The challenge may seem frivolous but in fact is a great example
of how prizes and network technologies can combine to collect and use
highly dispersed information–a problem of very general interest and relevance.