I guess Nvidia fired back at this during GDC, announcing their version using the Havok FX physics stuff. However, the way I understand it the game you play has to exclusively support one of the various standards and the Nvidia version actually takes processor power from the GPU to run. In fact the Nvidia version when used in on SLI will render with one card and do physics calculations on the other!? Personaly I would much rather prefer running an independent PCIe PhysX board and sacrifice no video processing.
The 2 differing standards are fairly pointless to debate however as the game must be programmed to utilize what your playing. Thus the decision has sort of been made for us.
Information on the Nvidia system with havok FX
http://enthusiast.hardocp.com/articl...ZW50aHVzaWFzdA