With the new Nvidia 310.14 experimental driver I have essentially no backlight on my laptop screen. xbacklight and xrandr report the brightness as 100%, but its literally like the backlight is completely turned off.
I don't have this issue on any earlier versions of the Nvidia driver that I've tried.
Brightness is fine with an external screen.
I've got a Quadro FX 570M in a Compaq 8510w.
Running Ubuntu 12.10