I just opened a new tab for Khan Academy so I can actually understand my Calc homework. Very cool video. I've heard about other schools (particularly one in NY) that have switched to this type of interactive online learning. The effects have been great. http://www.freakonomics.com/2010/05/12/freakonomics-radio-how-is-a-bad-radio-station-like-the-public-school-system/Here is a link to the Freakonomics podcast about it.
This is great website, I have been using this website for the past 2 years if I had doubts in Math or Science and it has never let me down.