My experience for what its worth: After installing the 320.18 driver I have had the same stability/artifacting/multi-color manifestation problems as others have reported in this thread. These issues (no issues before latest driver install) cropped up in Battlefield 3 sessions typically 45 minutes to an hour in. I do not have Metro or some of the other games that have reported to show similar problems with this driver, but in addition to playing a lot of BF3 I have been playing a lot of Shogun 2 of late, which has been working fine throughout. So since it was just Battlefield 3 that was an issue, I assumed the problem was something on the driver side, and not a question of the integrity of my actual card. From reading this thread and the one on EVGA's forums, I realized I was guilty of a lot of the installation missteps (installing Nvidia Experience, choosing express installation, not closing Precision or RTSS), so my first step was to remove the old files and perform a clean install. Unfortunately I believe I failed at doing this properly, as the artifacting reappeared upon my next BF3 hour session. Took a more drastic step next by performing a clean install of Windows 8 on my SSD just to be sure I got rid of everything. Finally, after re-installing a few necessities (sound card driver, etc.), 320.18 (a clean install this time with no experience & no RTSS), and BF3, a 3 hour play session last night went unhinged, with zero artifacting of the predominately purple variety.
In short, it appears that at least in my case user error and ignorance was to blame for the issues with this driver, and that when the old driver/ Nvidia Experience was removed from the PC completely the game performance at least, reverts to just as it was with prior drivers.
*Running a single gtx 670 FTW 2gig on 1920x1080 btw. Settings were never clocked beyond what came stock from EVGA besides modifying the fan curve for better temps.