http://www.washingtonpost.com/blogs/answer-sheet/post/how-well-does-khan-academy-teach/2012/07/25/gJQA9bWEAX_blog.html
This tough critique of Khan Academy by Christopher Danielson and Michael Paul Goldenberg gets at something near to my heart: the resistance to building a curriculum upon established research. They quote Khan: "I think frankly, the best way to do it is you put stuff out there and you see how people react to it; and we have exercises on our site too, so we see whether they’re able to see how they react to it anecdotally."