PC Perspective have a preview of the AGEIA PhysX Physics Processing Unit.

What AGEIA and even game developers envision a PPU will enable for a gamer is a world with physics unlike anything we have seen in a real time game before. We are talking about thousands of rigid bodies, real flowing water, hair simulation, avalanches of rock, clothing simulations and more. Even more impressive is the idea of a universal collision detection system that allows you to interact with absolutely ANYTHING in a game world. All of it calculated in real time with nothing scripted in the game engine.

** UPDATE **
The Inq has also had the chance to play with one of these cards. Click here to see what they think.