I'm going to offer a contrary opinion here and say that while the work is technically impressive, it's also crap. It's purely a case of "if the only tool you have is a hammer, everything looks like a nail". It is also NOT just HTML and CSS. Most of the real work is done in JavaScript. Given that, you might get better performance writing a software rasterizer that puts the whole image into a single rectangle and put that on a single div without 3d transforms. Another more "pure" implementation would use XSLT to convert XML into SVG with 3d transforms along the way.

What we really see here is a JavaScript 3D engine with a CSS backend. Impressive - yes. A good idea - not so much.