Damselfish--your point is well taken that the AOW class should be used to improve diver skills. I think we differ on what constitutes "diver skills." Any decent U/W naturalist class should emphasize protecting the marine environment with a strong emphasis on a diver's impact (buoyancy skills) on the reef. By understanding the delicate nature of corals and sponges (often thought of as "rocks" by some boneheaded divers) divers become more skilled and are less apt to damage the reef. The proof is in the pudding. I've had dozens of students thank me for making them better divers (at the conclusion of my U/W naturalist class).
I think that saying "you would do as well buying a book," is an unfair generalization. What "book" would that be? The Reef Set would certainly be helpful, and I feel all divers could benefit from becoming familiar with all the volumes, but which book would you be speaking about? Some instructors (myself included) pride themselves on a vast knowledge of the U/W world, and feel that they can pass this knowledge on to their students, making them better (and more appreciative) divers. Aside from a bachelors degree in biology with a concentration in marine biology I have done thousands of dives where I've learned quite a bit about the natural world. I don't know of any book that can pass on this type of knowledge and provide the experiential learning that the U/W naturalist class can provide.
All that being said, there are instructors out there who read & teach straight from a teaching outline and view the class as a way to line their pockets. Any student would be wise in questioning their instructor's credentials for teaching this course.