Mac OS X 10.11.6, Nvidia GT750m 2GB, OS X Built in drivers (310.xx.xxxx) as well as Nvidia Web Drivers (346.03.15f03)
Mac OS X 10.11.6, Nvidia GTX580 1.5GB, OS X Nvidia Web Drivers (346.03.15f03)
Mac OS Sierra GM 10.12, Nvidia GT750m 2GB, OS X Built in drivers
Short description of error
GLSL Viewport rendering is broken, has artifacts & glitches. Material Nodes don't work properly. OS X bug only. Checked on Windows & it works fine. (on 2.78RC)
Based on original file/post: https://cgcookie.com/2015/05/20/pbr-in-blenders-viewport/
Exact steps for others to reproduce the error
Open attached blend files to see the artifacts, OS X only, or see the screenshots.