I agree that NVidia PhysX is beautiful, and looks nicer in most games. BUT, I don't agree that it is a necessary aspect of many games. Matman:AA and MAfia II are th only games i play that support it, and I'm using an AMD 6950 (flashed to 6970) and an NVidia GTX 275 as a dedicated PhysX card. I would recommend using the custom drivers located at http://www.ngohq.com/graphic-cards/17706-hybrid-physx-mod-v1-03-v1-04ff.html. If you are choosing from scratch, and have never had an NVidia card with PhysX support, I recommend getting the NVidia card. Otherwise, you can use the custom patch for PhysX on AMD GPUs
PhysX, when CPU accelerated, is far worse than GPU accelerated, in FPS. Cuda is rarely used by the majority of people, I only use it to encode videos files into Ipod format. I also feel it isn't as fast as my CPU, but it sure takes the workload off of the CPU, allowing me to do other things on my Radeon 6970/Core i7 920