Here is an interesting video about Sal Khan, of Khan Academy, who has the most popular (or one of the most popular) educational video channels on the Internet. 

There were some interesting comments from the audience. 

It is better to just see the blackboard and not a teacher.
The teacher is a distraction, and can even create pressure or tension.
We can go back or fast forward, as we wish.
Sal goes through the explanations simply and in an unrehearsed fashion.
He is logical and relaxing. 

Check out his videos. I would like to do something similar for languages. Does anyone know what the best “blackboard” software would be? I am a messy writer and would rather type than write. Any advice?