This shows how far the browser has to go....was it just me, or did your browser start to choke while rendering this? It rendered it fine, but I could tell that the DOM was being abused heavily. I don't mean that in a bad way, but it just felt very 'heavy'. On the flip side, this is awesome that the browser can do this - and it's awesome that browsers can do this.
The DOM is not being heavily abused; it's just a canvas element and nothing else. The demo is so CPU intensive because the code is drawing the rasterized image pixel by pixel on the canvas, instead of relying on the GPU and using WebGL which would, AFAIK, result in much better performance.
One positive effect of doing this is that the code is _very_ portable and doesn't require any crazy feature in the browser or the PC (for example, i'm able to see the demo on my work computer even though WebGL doesn't work on it because of lack of drivers).