The New York Times highlights the potential of online science courses in "At 71, Physics Professor Is a Web Star". At MIT's famous online course site, physics professor Walter H. G. Lewin explains concepts like momentum, the conservation of energy, and the refraction of light. His presentations apparently have wide appeal to both in-class and long-distance students -- physics teacher in India, a student in Iraq, and a florist in San Diego.
The professor says he enjoys teaching introductory classes because "what really counts is to make them love physics, to make them love science." He's apparently very successful. He's also thoughtful about presentation. The Times says Lewin spends "25 hours preparing each new lecture, choreographing every detail and stripping out every extra sentence".
I love my online course on FDA. ["Introduction to Regulatory Affairs" in Advanced Academic Programs at John Hopkins (410.649)] I was worried I wouldn't get to know my students, but the fact that they MUST post means more work for both teacher and student, but also means no slouching in the back of the class. If they don't understand a concept, I know right away and can correct the misunderstanding. The trick is no points of for failing to understand - they have to feel free to post thoughtfully without being right every time.