ever since atari's "asteroids" simple inertia model, my brain's been fascinated by playing with physics in games. many games followed; the most fun for a while was in flight sims. ultima underworld was superior to wolfenstein in many ways; it had rudimentary 3d physics. then system shock, and trespasser, while somewhat cludgy, were a ton of fun. etc.
boing-boing today linked to a half-life 2 mod where you can play with virtual dominoes.
physics processors are now being sold. i doubt they'll catch on in PC games for a while, but i'd buy one if a decent game supported one.
playing with physics is fun!