At the end of Feb., I attended Mike Hagen's CLS class in Los Angeles, and the next day Winston Hall's advanced class in Fountain Valley. Both were extremely beneficial and worth every penny. After using both the SB-900 and SB-600 for over a year, I feel that I now truly know how to use them, and have more ideas about how to improve my range of photography opportunities in lighting.
Last summer, I also took Winston's two day class on my D300, and I learned more about the camera in the first hour than I did in 18 months of trying to figure it out.
I can hardly wait for the next classes in LA, and highly recommend any of the classes in your areas of the US.