I just installed the latest 196.75 driver for Windows 7 x64 version, and it seems to break OpenCL. The NVCUDA.dll (both 32 bits and 64 bits version) does not have the necessary clIcdGetPlatformIDsKHR function, although other two functions (clGetPlatformInfo and clExtensionGetFunctionAddress) are still there. So now I can use ATI’s OpenCL but not NVIDIA’s OpenCL (I have both ATI and NVIDIA cards on my computer). I hope NVIDIA can fix this problem soon.
[EDIT] I resintalled the driver and the problem is now gone, so never mind :P