Unfortunately the game was taken down due to the Japan situation. Understandable.

Under Safari i was able to simulate ~80 live physics objects in a high collision environment at full frame render, bound to the DOM at 60fps on reasonable hardware 6 months ago (safari still has the fastest DOM paint time out there now).

Even when using Firefox 3.6 i could manage around 20 dynamic objects.

No CSS3 animation, just math and re-paints.

Javascript Math is not slow (at all), its generally the DOM/Canvas slowing you down.