Some of the PhysX content I've seen looks really good now it's on the GPU and you know how critical we were of PhysX on the PPU card... it was pants. And Ageia had no installed base, which meant no games could use the effects in such a way that'd break gameplay if you didn't have the PPU add-in card. We'll have to see how good it ends up being when it's actually shipping code running PhysX on the GPU now there's a big installed base behind the engine (70m+ CUDA GPUs). Havok has had some great implementations in the past, but I can't help but feel a large portion of the engine really needs to be accelerated on the GPU to get the best performance/most realistic effects. The CPU will still be used for certain effects, but not all, because it's a better fit in some cases.