I’ve just got a new iMac with a NVIDIA GeForce GT 750M 2 weeks ago and I’m trying to activate GPU rendering for cycles, but in System/Compute Device don’t let me choose anything more than CPU. No idea why. It happens in both installed Blender versions 2.74 and 2.75.
Also, although not sure if is related, in Blender 2.75 all Add mesh extra objects menu for customize an object are not activated and unuseful (in 2.74 works).
Concerning the greyed out primitive settings, try enabling “Global Undo” under User Preferences > Editing.
As for the CUDA thing - sorry, no idea. But I doubt that you will see much of a performance gain from a notebook-class graphics card anyway, especially if it is only equipped with 1 GB VRAM…
@ Noke, i just updated to CUDA driver 7.0.52 and it works just fine
Regarding the future of Blender on Mac, i don’t see any problems.
But putting pressure on Apple to fix things needing to be fixed and asking for better things is always good.
It would be nice with an affordable external thunderbolt GPU box just for rendering purposes.