Collision response is somethign I've been working on and off with since last summer. It can fill all your time all by itself
Physics in 2.5 are rather slow, especially with more bots on the screen, but definately solid. However I should be able to optimize it to run at least as fast as 2.4.
Point is it's a terribly bottomless pit that I wouldn't recommend tinkering with if you value your sanity