Khan isn't going away.

but he really needs to improve his methods and style.

Methods: as many have noted using the #MTT2k hashtag, a lot of Khan's videos have subtle "errors" in them.  I say that with quotes since few people who aren't teachers have any idea how damaging it can be to overall learning when the teacher doesn't really understand things himself.

A glossed-over explanation can leave a kid frustrated and puzzling over something for the whole period or more, which doesn't bode well for learning anything else that day. Worse, it often gets in the way of truly understanding all of the material built upon it.

Style: He really needs to prepare more thoroughly for his videos.  A couple of minutes on Google and wander into the closet/studio doesn't cut it. It's not the specific facts that are wrong, it's that Khan has little idea of the vast context of those ideas.His explanations and demonstrations are good to a point but they suffer from the same tunnel vision that a student's book report written the night before the deadline does ... a few quick facts, a pithy statement, and you're never quite sure whether he has understood or just regurgitated the Cliff's Notes.

A video on quadratics and factoring contains a problem that he changes in the middle ... the coefficients aren't what he wanted to demonstrate his point, so he switches on the fly.  I have no problems with a teacher doing this in the classroom, but when you have the ability to simply stop the recording and begin again on a 10-minute video, you should make the better video.

CBS News: Demonstrating situational irony since 1928.
Graphic: dy/dan

Interaction: The biggest argument against KA is that students are supposed to be in class, interacting with teacher and other students, not staring blankly at computer screens with headphones blocking out the world, mesmerized by the little moving cursor and the trails of color on the black canvas.

This, for me is the biggest problem.  If I am being hired to teach, then I should teach.  If you want the benefit of my thirty years of experience and are willing to pay for it, why would you ask me to make a generic math video the focus of the classroom while I sit and "monitor" the teacher's dashboard or wander around doing nothing. Augment with KA after school or at home, but don't allow it in the classroom.

Bottom Line: Khan is worse than a decent teacher and definitely worse than a good teacher. Khan is better than a lousy teacher and definitely better than no teacher at all.

If your student wants to learn on his own, let him. W3Schools, Khan Academy, Purplemath.com ... they're all awesome and can be accessed at home for free. If, on the other hand, you need KA in your classroom in order to be effective, then get the hell out of teaching because you're a disgrace.