AMD has released OpenCL 1.1 drivers with the ATI Stream SDK 2.2; a release 2 months after the specification release. nVidia has an OpenCL 1.1 drivers but only available for nVidia registred developers.
So far, I haven't seen really good results of OpenCL benchmark on AMD. I don't really know if it's a hardware limitation or a lack of optimization of the drivers or maybe both. Some people will say that nVidia have a more advanced cache system but this is not true on GeForce 8/9 hardware which remains really efficient. One think is sure, nVidia has more experience through CUDA and their OpenCL implementation is built on top of it.
With the progress of AMD on OpenCL, I guess it's going to be interesting to observe OpenCL benchmarks in the next months!