I'm wondering if OpenCL is supported for OS X for Houdini 14 and Flip/Pyro – it's in the settings for flip solver and pyro solver but I get the same frame rate when
I enable it on 12-core Mac Pro with dual FirePro D700

Try with OsX Yosemite - on a Amd 7950 there is a significant difference.

I'm on OS X 10.10.1 (Yosemite). Is there some log I can check for errors or confirmation that it's working?

Try the ‘dop_example_opencl1’ search in the documentation for ‘OpenCL smoke’

Setting the' Uniform Divisions' on the ‘Smoke Object’ to 250:
3.5fps using OpenCl vs 35fpm(~0.5 fps) without.

OsX 10.10.1 Amd 7950, dual 6-Core Xeon @ 3.33

In the About Houdini, scroll down and you should see the OpenCL info:

OpenCL Platform Apple
Platform Vendor Apple
Platform Version OpenCL 1.2 (Sep 20 2014 22:01:02)
OpenCL Device AMD Radeon HD 7950 Compute Engine
OpenCL Type GPU

ah - ya, that's working. with 60 uniform subdivisions I get 15FPS for OpenCL and 9.5 for 12-core/24-thread CPUs. Nice

But are you using both GPUs?

Houdini currently will use one GPU - I'm wondering if the trash-can Mac automatically uses the other GPU for OpenCL processing though.

There is an environmental variable to use ‘HOUDINI_OCL_DEVICENUMBER’ that can select the GPU. You can set it in the houdini.env file, and I assume it would then have more memory than sharing the GPU with the display.