Cool, but note that the rendering is ultra mega slow. Even if you get the "compilation" process to be faster, browsers are really slow when it comes to box-shadow. If you upload an image, then scroll to the bottom and back to the top, Chrome takes like 6s to re-paint the page.
Yeah, probably not very useful for photographies.
I'm thinking about using it for pixel art animations. Since the browser can animate each box-shadow position and color, we can create fancy transitinos. I will upload a proof of concept of that this weekend. :D