I like Khan Academy, I think that it is good collection of videos and an excellent tools for students to develop their procedural maths problem solving skills. I do not however think that it can be at present a complete Maths Education. There are some students who do not learn effectively from lecture presentations (even ones they can control the pass of). There is also a need to develop skills in application of these maths skills to real life problems. As a teacher I find the ability to track student progress in their skill development useful and mush more insightful than just setting an end of topic test.
Fell free to ask questions about Khan or my presentation in the Comments.