Reply to Sean,
Some professors seem to think that lecturing about material that isn't presented anywhere else will force students to attend class. But in my experience it also creates a class that takes notes furiously rather than engaging the material and asking questions. Overall, I think it's a counterproductive strategy.
At the other end, if the professor *only* lectures on what's in the book, what are they being paid for? Just talking? Better would be for the professor to lecture on application, the what/why (and not the how), how ideas are related, anecdotes and the like.
