TITLE: What does Khan Academy have to offer? Depth? Rigor?
QUESTION [25 upvotes]: Khan Academy - http://www.khanacademy.org/ - is often cited as a great online resource for learning mathematics and other subjects. I have heard many good things about this website and was wondering in what depth are subjects covered? 
I know Khan covers topics in (highschool) algebra and calculus. What other subjects are treated? and at what level? How rigorous is his treatment?
Some background: I teach at a university and would like to know if this is a good resource to point students to. I'm thinking primarily of students who are having trouble in college algebra, calculus I, etc. Not necessarily math majors.
To be crystal clear: I'm not looking for suggestions regarding other online resources. I just want an honest critique of Khan Academy from those who've explored what it has to offer.

REPLY [2 votes]: I use Khan Academy extensively with my own children and (together with friends) to help kids in Newark, NJ. Khan is much different in practice than what it looks like on the surface.
Khan has lots of bite-sized video lessons that are well-produced (even when you only see a simple blackboard). They range in quality from pretty good (most of the math) to excellent (browsed through some amazing musical theory and social science videos). Khan is judged on the videos, but they're almost besides the point.
Computer-based education is only clearly superior in mathematics only (so far). This is because computers are far better-suited than teachers or books to:

Move at your pace
Allow guessing before learning to prime you for what's coming
Provide time-spaced learning to ensure knowledge sinks in
Check for mastery before allowing you to move forward
Motivate via gamification
Probe previously-mastered areas for weaknesses
Help coaches to check for appropriate progress

The videos, while very helpful, are only a last resort. You should only watch the video after first guessing and then using the written hints. 
Khan is amazing in the areas covered by exercises. Khan is far less effective in subjects with videos but no exercises (higher areas of linear algebra, calc, etc.). I expect Khan to gradually expand their coverage and it already seems like a superior alternative for non-math/engineering majors.