More and more rumors point towards a big showing of OpenCL at the MacWorld 2009 from Apple. We already reported that rumors point towards an early release of OS X Snow Leopard supporting OpenCL.
With OpenCL the NVIDIA GPU can be used in parallel to the CPU offering possibly dramatic performance increases.
New rumors point to iMac and Mac mini updates that bring NVIDIA GPUs to these systems. New iMacs have been missing in the release of the new Apple computers in November.
If Snow Leopard with the OpenCL support can show substantial performance increases, Apple would be in a great position to sell the latest NVIDIA enabled generation of hardware in a big way.

About OpenCL:
OpenCL (Open Computing Language) is the first open, royalty-free standard for general-purpose parallel programming of heterogeneous systems. OpenCL provides a uniform programming environment for software developers to write efficient, portable code for high-performance compute servers, desktop computer systems and handheld devices using a diverse mix of multi-core CPUs, GPUs, Cell-type architectures and other parallel processors such as DSPs.
More details on the Khronos site.