Aside from the known limitations of the Nouveau Kepler Gallium3D support with this "NVE0" driver, overall it worked out pretty well. In the very early testing of this driver, there was the bug that filled up the entire disk drive, but that is now fixed.
Without proper re-clocking support for Kepler, the overall OpenGL performance compared to the official NVIDIA Linux driver is quite slow. Regardless, here are some early benchmarks of the GeForce GTX 680 with the open-source driver from the Linux 3.4 kernel and Mesa 8.1-devel. The GTX 680 performance is being compared to the NVIDIA 295.40 binary graphics driver.