There is a generic problem with mechanisms of this nature: it is difficult for a crowd to learn. I saw an excellent example of this at the Festival of Lights in Lyon earlier this month:

During one exhibit, there was a giant game of 'breakout' (http://en.wikipedia.org/wiki/Breakout_%28video_game%29) projected onto a large ferris wheel. The crowd was supposed to play it by all waving orange lights. If you remember breakout, you know that there is a limit on the speed at which the bat is allowed to move, so if you let the bat get too far from where the ball is going to be, there will not be enough time to fix it before the ball hits the floor. It was impossible for the crowd to learn this, however, because an individual in the crowd gets no noticeable feedback from their actions once they have been averaged with those of the rest of the crowd.