This is great stuff, easy to follow along even for a dabbling novice like myself. I've always been interested in simulating light, and wrote a paper (and shader) in high school about simulating sub-surface light scattering effects. I remember when I had saved up enough money to buy H. W. Jensen's book on photon mapping, and spending countless nights trying to decipher what it said. It's actually a very good book, but the maths was way above my head in high school – still is, actually.
Any way, great work, and beautiful demo! I've spent more time playing with it now than I should have, and work is suffering for it. I regret nothing! :o)
Jensen's Photon Mapping was also my very first exposure to light transport theory - I was in high school too and got the book as a Christmas gift. The math was way beyond me at the time, but it was the first time I realized computer graphics actually had some substance and wasn't just about making triangles fly around funny. Definitely a very influential book for me :)
Any way, great work, and beautiful demo! I've spent more time playing with it now than I should have, and work is suffering for it. I regret nothing! :o)