I have begun to more systematically think about how the 36 Learning Principles noted by James Paul Gee (2003) apply in the range of games we have been exploring during the IDGBL course, and in my own studies of space-themed and related fantasy games.
For convenience I placed a web summary of the 36 learning principles at
http://atate.org/mscel/gbl/gee-36-principles.html
For my game review I also established a questionnaire to survey the use of the principles in a game, and it works more generally now for any game. See
http://atate.org/mscel/gbl/gee-36-survey.html
World of Warcraft has very many of the attributes advocated by Gee. And I can see WoW gives an educator very many ideas for how to employ those principles in a game-oriented experience. BUT, I am less positive about the use of WoW itself for education directly.
Reference
Gee, James Paul (2003) What Video Games Have to Teach Us about Learning and Literacy, Palgrave Macmillan: New York. Second edition in 2007.