Set NVreg_ModifyDeviceFiles to 0 can deny common user direct access /dev/nvidia0.
If it set, you can see "direct rendering: No" in glxinfo.
But it will make gdm cannot start at some distribution.
Centos 6.3 64bit with nvidia 295.59 will exit after print [*] Abusing nVidia... without other message.
I don't known why... (didn't set NVreg_ModifyDeviceFiles=0)