The NVIDIA GK106 core is the graphics processor within the NVIDIA GeForce GTX 660. The GeForce GTX 660 has a 980MHz core clock, 1033MHz boost clock speed, 2GB of GDDR5 video memory, 140 Watt TDP, and a retail price just over $200 USD. This GPU was launched back in September and supported by the proprietary NVIDIA Linux graphics driver from the same day, but is only now being brought up within the reverse-engineering Nouveau community.
While basic support is there for the GK106, that's about it. Skeggs wrote in the commit, "Modesetting seems to work alright, as does graphics (using binary driver fuc from nve7...)."
Aside from needing to use the binary driver's FUC microcode -- a pain to extract for novice users as before getting any accelerated support you must first install the NVIDIA binary driver and use MMIOtrace to dump your own firmware for the code -- there's other shortcomings too. Skeggs additionally said in the commit message, "Lots to be done no doubt, but this'll get an image on the screen for people."
This initial GK106 Nouveau support will likely be merged into the Linux 3.8 kernel.
Overall the NVIDIA GeForce 600 Kepler series support is still quite primitive with Nouveau when it comes to OpenGL acceleration and decent performance. There was same-day NVIDIA GeForce GTX 680 Nouveau support but it required using the binary FUC microcode, the GPU clocking was a mess, and there were other problems. To this day it's still not too good unless you just care about mode-setting. If you're shopping for a new NVIDIA graphics card to use with Nouveau, see my 2012 Linux hardware holiday shopping guide.