I'm no Peter Norvig, but this is the discussion section after all....

One tool that may or may not have a place in online education is gamification. To put a long story short, the gaming industry has gotten plenty of practice motivating people to keep going, even at tasks that wouldn't necessarily be the most interesting. Other industries have finally noticed this, and started trying it out to see which concepts from gaming carry over well to other fields. I don't personally know of any research specific to education, but would be interested if anything relevant was found

An enthusiastic, low-level introduction to gamifying education: http://www.penny-arcade.com/patv/episode/gamifying-education