One of the brilliant things about Khan Academy is that it allows teachers to "flip the classroom"—what used to be lecture is now watched at home at one's own pace (with freedom to rewind), and former "homework" is now done in class with the teacher providing assistance.
In addition to videos covering math (basic addition through pre-calculus), there are other videos on history, finance, art, and more. Moreover, many of the math videos are connected to auto-generated problems sets which make it easy to practice the concepts. For teachers (Khan calls them Coaches), there is detailed information about students' progress.
As expected, there are detractors who fear a loss of jobs and who argue about whether or not drills are the most effective learning tool. My take:
An inability to cope with change makes for poor teachers. Teachers are students for life.
I tend to advocate a learn-by-doing approach for many subjects. Admittedly this is difficult in the humanities and arts, but I find that it is a lack of creativity rather than an inherent obstacle. For math, this involves doing a lot of math problems. The more instantaneous the feedback the better because waiting a week to see if your understanding was correct is absurd.
I do see merit in expanding numeracy education. However, Khan does take the time to explain what he is doing and the fact that kids (and adults who are using Khan as a review tool) are excited about learning (math!) while demonstrating improvement suggests this approach is working.
How Khan Academy Is Changing the Rules of Education at Wired for a length article.
The Importance of Numeracy for our discussion on numeracy.