This contest, which begins on December 5th and will award $40,000 to the first smart mob to locate 10 red balloons, is now posted on the Pentagon website:

To mark the 40th anniversary of the Internet, DARPA has announced the DARPA Network Challenge, a competition that will explore the roles the Internet and social networking play in the timely communication, wide-area team-building, and urgent mobilization required to solve broad-scope, time-critical problems.

The challenge is to be the first to submit the locations of 10 moored, 8-foot, red, weather balloons at 10 fixed locations in the continental United States. The balloons will be in readily accessible locations and visible from nearby roads.

The contest is further described in the New York Science Times today: Looking for Balloons and Insights to Online Behavior.