I love the idea of the Khan Academy, and support it, but I have not sat down and really tried to learn anything specific from them. Well, I take that back. My wife first discovered them back in 2008 during the finincial crisis, and wanted to understand exactly what a “Credit Default Swap” was and found Salman Khan’s explanation. Very clear, and it left me with a reasonably decent understanding of the thing.
So how many Dopers have used them?
I suggested Kahn Academy for a deaf student who was looking for a tutor. They love it.
I have been using Khan for math classes and like it.
I learned that revenge is a dish best served cold.
Khaaaaaannnn!!
I’ve worked on and off the site for three years. I just earned a 91% in my pre-calc course. I think it’s really helped me on my career change / augmentation path.
I have found it to be great for supplementing math classes. I watched a couple of the economics videos and they were good as well. I have heard some grumbling that he blows through some finer points at times or isn’t very rigorous. It’s free and the format is such that you can watch it on the crapper instead of Facebooking or posting on pretentious message boards, so I assure you it can’t hurt.
I’ve used it for specific topics that my kids were struggling with in school. For instance, my daughter asked at dinner tonight about natural logs and the “number” e. It’s been several decades since I even thought about stuff like this, so it’s nice to have some back up. It’s that, or the SDMB.
For a while there I was trying to relearn math, found it extremely helpful and even a little fun.
I used it through A&P and Microbiology and I really liked it. It was so much easier to stay engaged in the videos than my textbooks.
e is a number, not a “number.” 
I’ve found KA very useful for reviewing Calculus topics, especially the hairier stuff (double integrals and whatnot.)
And here I thought e was a letter. You mean Sesame Street lied to me!
I’m sorry, old chap, the what?