I have the exact same issues as everyone else (blank gem store screen, frantic spinning mouse). I usually run the client windowed on my Mac, but whether it’s full screen or windowed what has always helped was to Command-Tab to the desktop, clicking anywhere on the desktop with the mouse and then tabbing back to the client. Changing the focus seemed to help (not just command-tabbing).
My specs:
MacBook Pro
Retina, 15-inch, Late 2013
Processor 2 GHz Intel Core i7
Memory 8 GB 1600 MHz DDR3
Graphics Intel Iris Pro 1024 MB
Software OS X 10.9 (13A3017)