Backlight control problem with Nvidia driver

Hello!
I have a Sony Vaio VPCS11X9R laptop with Nvidia GeForce 310M graphics. The problem with my Ubuntu 11.10 (as with every other distribution) is that backlight is always 100%.

The solution worked for me is adding Option "RegistryDwords" "EnableBrightnessControl=1" line to "Device" section of xorg.conf.
However, it simply works from time to time. I can boot and have no problem or stick with 100% brightness again.
I have discovered that after returning from sleep mode, backlight becomes controllable again.

Nvidia driver version: 280.13.

What are the possible solutions to this, either with Nvidia or nouveau driver (it doesn't make difference to me, now I only care of backlight)?