I have similar second-hand experiences, but really I'm not sure it's different than any other self-study method in that regard. I know people who are doing spectacularly well in things they self-taught from textbooks and online materials (FAQs, tutorials, StackExchange answers, etc.), and other people who have quite serious misconceptions they've somehow picked up in that route.
Khan Academy is interesting to me not really because it's a revolution in learning, but because it's another modality that is better for some people. Some people learn well from written material, and those people have traditionally been the successful autodidacts, working their way through textbooks and tutorials. But perhaps different kinds of materials can cater to other people, with people working their way through a lecture series instead of a textbook. That'll probably have many of the same pros and cons.
Khan Academy is interesting to me not really because it's a revolution in learning, but because it's another modality that is better for some people. Some people learn well from written material, and those people have traditionally been the successful autodidacts, working their way through textbooks and tutorials. But perhaps different kinds of materials can cater to other people, with people working their way through a lecture series instead of a textbook. That'll probably have many of the same pros and cons.