I came across this site through an article that was on HN sometime last year, around November or December IIRC. Since then I've watched roughly 100 videos on that site. Some of the Finance videos, Trig, and Pre-algebra as a refresher, and I'm now roughly 60 videos into the Linear Algebra videos. Even though I'm in the midst of my master's program now, I've set a goal to watch 2 video's every day as time permits.
I am so impressed with this site, and with Salman Khan. The math is very well done, but it's also very approachable. Most of the videos are roughly 10-15 minutes in length and are highly topical. That makes it easy to jump in and pick up a refresher on something you haven't seen for a while. It's also great for getting into something you haven't ever seen before. Personally I haven't ever had Linear Algebra before, and if you've looked at many of the textbooks, they are pretty dense, particularly if you are self learning. I've found this site to be a great resource in getting oriented and it has really helped me get some traction.
I have recommended this site to dozens of people, and while most of them don't share my love of mathematics, they have been able to get some traction in various problems by using this site as a supplement.
Anyway, as a daily user of the KhanAcademy, I can't say enough good things about the site. I don't think it's a stretch to say it has the potential to revolutionize how math is taught.
The one downside to the site I've noticed is the lack of problems sets. There is a tester that will walk you up through the different topics, but unlike the video's you can't just start where you feel you need to, you have to work up through the early material, and that's fairly time consuming. I have a number of other resource's I'm using for problem sets, but it would be nice to have a few problems to work through for each video.
Overall an absolutely fantastic resource.
If you think otherwise then I'd really appreciate a suggestion, as I have someone I'd like to point at it ...