Does any OS X hardware contain on chip h.264 encoding/decoding?
Apple's own apps on OSX has video acceleration support for years, provided by the GPU. h.264 hardware video acceleration is available to 3rd-party apps via the Video Decode Acceleration Framework since OSX 10.6.3. See:

http://developer.apple.com/library/mac/#technotes/tn2267/_index.html

http://arstechnica.com/apple/2008/10/digging-into-new-macbooks-support-of-gpu-accelerated-h-264/

http://xbmc.org/davilla/2010/05/03/osx-gets-h-264-accelleration/