Richard Carey points to an outstanding article by Shane Snow on using game mechanics to power your business over at Mashable.
This rings true in my personal use of social media (see here re Foursquare) as well as in a lot of the thinking that has gone into what will happen to learning materials as they migrate from print to digital.
The one thing missing from the article that I think is a critical element is narrative thread. Here are some comments of on how that applies to education.