I have installed the EVGA GTX 660 SC and it works good in Mountain Lion.
I first tried "GraphicsEnabler=No", installed the card and rebooted and I had initial display but OS X decided it did not recognize the Nvidia Rom.
I tried to play with the bios settings and boot uptions.
I tried to come back to the Intel 4000 which worked fine before without success.
My goal was to boot up and try the Nvidia drivers.
I had to completely remove the GTX 660 to allow me to boot again.
I installed the latest Nvidia drivers, made sure I had "GraphicsEnabler=Yes", turned it off, re-installed the GTX 660, rebooted and voilà.
I left the bios settings at auto, I think.
I had fun for a couple of hours and I got to bed very late last night but I made it finally.
I now have a working graphics card and I am very happy.
For a while I thought I had waisted that money.
The only strange thing so far is that when I shut down, it turns off but will turn back on again, it does a restart.
Not a major problem but annoying because hitting the power button is not practicle, so I will hit F10 to go to the boot menu and then I turn it off manually.
Here are my system configs:
Case Cooler Master Elite 120
Intel DH77DF mITX board
i3-3225 with Noctua NH-L9i
16 GB Patriot RAM 1600
EVGA GTX 660 SC 2GB
PSU Corsair CX500
Samsung 840 Pro 128GB SSD for OS X
WD Black 2 TB for data and backups
I am also adding a new Intel 240GB SSD which will contain Windows 8 Pro so I will have the two OS in the same PC.
I got the GTX 660 on sale for 215$ including a free copy of Assassin's Creed 3.
Good card for the price and it works using Nviidia's drivers.
I hope this helped.