I actually found it in the print edition in one of the last Sunday Times, but it's been covered elsewhere, too:
Salman Khan worked as a hedge fund manager when he started tutoring his cousins over email and phone in maths. Then he tried out Youtube clips - that was so successful that he eventually quit his job to do this full-time. All the clips are free, so if you fancy doing a bit of maths, or want your kids to get better at it, or want to learn something else, you can find them here:
Here's his story: