I would bet good money that there will be few this little tidbit will affect, but NVIDIA has apparently disabled support for PhysX processing on its GPUs when an ATI GPU is present. This would only affect users who have an NVIDIA card installed for PhysX and an ATI card for graphics.
A poster on the NGOHQ forums received an email reply from NVIDIA support explaining the issue. NVIDIA says in part that the issue had to do with some "business reasons" along with quality assurance reasons. This apparently happens with version 186 and newer drivers.
The full email reads:
Ill explain why this function was disabled.
Physx is an open software standard any company can freely develop hardware or software that supports it. Nvidia supports GPU accelerated Physx on NVIDIA GPUs while using NVIDIA GPUs for graphics. NVIDIA performs extensive Engineering, Development, and QA work that makes Physx a great experience for customers. For a variety of reasons - some development expense some quality assurance and some business reasons NVIDIA will not support GPU accelerated Physx with NVIDIA GPUs while GPU rendering is happening on non- NVIDIA GPUs. I'm sorry for any inconvenience caused but I hope you can understand.
NVIDIA Customer Care"