I have to say it is nice to look at. [Firefox, OS X Lion, Core 2 Duo] Uses about 15% CPU, but after a while the fan has to kick in because there is some serious number crunching. 

There is however, very little data required for download and execution of this demo. Unless the client hosts all the data needed to run a proper simulation, such graphics programs can only be defined parametrically. Alternatively, one could perform the simulation where the data is and stream 2D or 3D to the web browser.