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
A week ago Google launched an open source project called Course Builder it packages the software and technology used to build their July Class Power Searching with Google. The discussion forum for it is here. Tomorrow is the first live hangout where he will be answering questions about MOOC design and technical aspects of using Course Builder. The live hangout will is scheduled for the 26th of September.
A small group of us has been working on related matters but we are far from done reviewing the relevant literature. Not having any good questions yet, I thought what harm might there be in asking for the broader community to come up with a few questions! If Norvig has answered your questions in some of his other existing material that I've reviewed I'll respond with a link.