+1 to the "high course join, low course completion" crowd.
One thing that I did at work was establish a betting pool with two other co-workers on the Coursera C++ course that finished in December - completers would collect from non-completers. That is my one Coursera completion.
I'm pretty sure that attaching betting pools to MOOC sites would make a major difference to completion rates for participants.
It almost never carries voting rights.