I don't have a problem with Khan's site existing, but it's disappointing that often answers to requests for learning materials/ideas begin and end with Khan Academy. My personal opinion is that Khan's videos are roughly comparable to an average-quality classroom teacher lecturing about a typical mediocre curriculum.

They have some significant advantages compared to (just) a classroom: (1) They set a quality floor – sometimes a teacher can be really incomprehensible, or mean, or whatever, but Khan's videos are consistently okay. (2) They are available from anywhere, without need for special social/technical infrastructure, like enrollment in school or access to a university library. (3) They are self paced, which means they can better accommodate the various interest level, motivation, and speed of different students. (A typical classroom also has some advantages: it gives social setting, a consistent schedule/structure, and human feedback.)

I'm also disappointed though, because it seems like, given production resources, there would be potential to make widely available materials that were much better than average lectures. With significant production effort (a team of subject experts and content creators doing a lot of dedicated work on each topic) I think it would be possible to make something truly great, but Khan's videos fall so far short of my imagination. For any particular topic, there are typically other freely available resources which I think are better.

I've also been disappointed because many people have hyped the site as being extraordinarily amazing, but when I have looked at it, what is there doesn't match the hype.