Mazur is a fine speaker, but he fails to mention an important thing which importance is underestimated - teaching good students. Students who are smart, interested and willing to learn can be just as easily harmed by bad teaching (or helped by proper teaching, for that matter). Sadly, many people seem to think that teaching good students doesn't require much attention or conceptual thought, since they would learn the subject by themselves anyway. Quite the contrary, excellent students require more attention precisely because they are more capable, so there is more potential to be tapped by a good teacher.
Teaching gifted students is, IMHO, more difficult than teaching mediocre ones, but also more challenging, since it's difficult to make general statements and it's not obvious what the right approach is (in the case described by Mazur, we more or less know the "right" way of doing things - understanding instead of memorizing, thinking vs mindless application fo recipes etc.).