ATI has officially announced today (at Computex) their plans to bring "Boundless Gaming" to the world. CrossFire users will be able to use 1 card for graphics and 1 for physics OR 2 cards for graphics and 1 for physics.
You can read [H]ard|OCP's take on it.
Heads up! At the bottom of [H]ardOCP's article there is a zip file that contains a very nice pdf from ATI with tons of details on their physics processing solution.