Using OpenCL to offload the CPU will be very application specific. And initially at the 10.6 lauch, it will be of no or no help since few if any of the applications that you run will have been rewritten to use OpenCL.
It may be useful for a few use cases (e.g. video playback), but in general an Atom + OpenCL won't match a good quad core desktop.
I agree, but many that buy a Mac Mini would be happy enough with Apple's software at the get go. I could see Apple rev'ing all the OSX shipped apps (QuickTime, Safari, Preview, Finder CoverFlow, etc) to take advantage of OpenCL or at least the ones that would need to take advantage. iLife and iWork could be rev'd for Snow Leopard as well come the Mac Mini's release.
I would not be surprised to see a similarly packed Macbook Mini (Apple's Netbook). Jobs always poo-poos markets Apple is about to enter and they did it with the Netbook niche. It is guaranteed that Apple will release a Netbook this year. Apple has said time and time again that notebooks (including netbooks) are the future. It's gonna happen.