Since the release of Snow Leopard, David Gohara from MacResearch has been working on some video podcasts about OpenCL.
The podcasts are based on commented slides with demos time to time. These podcasts target MacOS X and especially XCode and nVidia GT200 chips. It really is a in depth coverage based on code samples and GPU architecture.
Furthermore, a good part of the podcasts is dedicated to the questions from the previous podcast.
I highly recommend these podcasts! There are available through iTune or individual downloads.