I am only aware of a few users that use CFD on the MAC OS and most of them use the Apple Bootcamp.
For the few users that try to use Parallels, I would suggest that you adjust this setting to improve performance.
Turns out when you enter the virtual machine (parallels) the MAC default behavior is to go into an energy saving mode and more importantly, it "switches" graphics behavior.
This means that you need to go into 'Energy Saver' window and make sure that 'Automatic Graphics Switching' is turned off.
Here is the link that you can use to read the solution http://download.parallels.com/desktop/v5/docs/en/P