*Wouldn't it be cool if* a physics engine could be used to construct a working steam train? Afaik the components missing from today's physics engines are the notions of temperatures and pressures. Ok, yeah, the whole principle of a steam engine is pressure and temperature, but I think it'd be cool to have a train move with no rules other than those of physics...

On a completely different topic, my 3rd year Comp Sci project/dissertation has been revealed to me(2nd choice of 5):
RKM-1: Detecting Repeated Patterns in Audio

Makes a change from the 3D bandwagon :)