I'm working in Premiere Pro CC on OSX 10.8.4 and every once in a while my entire Mac will freeze/stall/hang for 1-2 minutes. During the freeze, the mouse cursor dissapears and the keyboard doesn't work. Once the freeze is done, everything resumes and works like normal.
Things that seem to trigger this event are adjusting effects sliders on layers that have transparency, alpha channels, or low opacity. I mostly work with Quicktime MOV files that have alpha channels and use fonts with an opacity set to 78%.
One time this even happened after I did an export media, and the preview window on the export media panel was stuck at "Rendering Preview".
I'm using one of those newer iMac machines and it has an NVIDIA GeForce GTX 680MX 2048 MB video card. In the project settings, my video rendering and playback is set to "Mercury Playback Engine GPU Accelleration (OpenCL)". I will next try setting it to CUDA to see what happens.