As proof of me having a seat on the Shaffer bandwagon before the book came out, please see here and here. David Williamson Shaffer is the latest of the GAPPS group at the University of Wisconsin to come out with a great book dealing with games and learning.
Shaffer's work really interests me because he focuses on the way in which people learn to act professionally - Shaffer defines "professional" in this instance to be "any kind of work in a complex domain that requires the exercise of autonomy and judgment."
Really tremendous stuff. You should start by reading Henry Jenkins 2 part interview with David here and here. Then check out the book's web site and then click on the prior posts I have to find links to David's older stuff. Well worth the time. I think David has a lot to say about how serious games can impact our world.