I have a colleague who has a machine with 4 NVIDIA Tesla cards, and he is looking at getting one with 8 cards.
Many video/audio editing tasks benefit from the GPUs, not to mention HPC (but OpenCL sucks, so its NVIDIA/CUDA only here). If you aren't into those workloads, maybe you don't want a MacPro.
That's a good point, and I could get extra mileage out of GPUs for some tasks. HMMER and Amber both benefit from that type of acceleration, for instance. But unfortunately I still would expect to be CPU-bound nearly all the time. Having 64GB of memory would have been great, but I'd need another 20 cores to fully utilize it.
Many video/audio editing tasks benefit from the GPUs, not to mention HPC (but OpenCL sucks, so its NVIDIA/CUDA only here). If you aren't into those workloads, maybe you don't want a MacPro.