I confirm the above. Same behavior with Vaio F11M1E (GeForce GT 330M) and

1) ArchLinux + xf86-video-nouveau 0.0.16_git20110316-2
2) Pure Debian Wheezy + xserver-xorg-video-nouveau 
1:0.0.16+git20110411+8378443-1
3) Fresh install of Ubuntu 11.04

In all three cases, Fn + F5/F6 work as expected until the first suspend/resume 
cycle. Then, brightness is not controlled anymore (restarting hal or acpid does 
not help).

Had to resort back to nvidia which, by the way, freezes my computer on 
suspend/resume with Gnome3 but works ok with Gnome3 Fallback in ArchLinux 
(nvidia 270.41.06-1) and works ok with Gnome2 in Debian (nvidia 260.19.44-1)...

Confirm the original report. Unlike the first reply, changing the brightness 
never works, even after booting the system.

Otherwise, the notification shows up and I can set the "brightness bar" up and 
down, with no visible changes to the actual screen brightness.

I'm hoping this is fixable, since the NVidia drivers seem to be causing 
stability problems in my system.

Hi, I would also like to confirm this issue on a VAIO VPCF11M1E with GeForce 
330m on an ArchLinux installation. Brightness is stuck on max after suspend and 
cannot be controlled.

I have managed to solve it by compiling a kernel using 
http://cgit.freedesktop.org/nouveau/linux-2.6/
(Note that this will be merged to mainline linux hopefully when 3.2 comes out 
or later)

Using a kernel from above I just appended acpi_backlight=vendor on my kernel 
command line (i.e. edit your GRUB/GRUB2/bootloader configuration and add it).

This removes the /sys/class/backlight/acpi_video0 interface and adds  
/sys/class/backlight/nv_backlight and  /sys/class/backlight/sony/ directories.

The former controls brightness, the latter does nothing.
Backlight Control works fine on boot and after suspend.

Unfortunately, the sony-acpid daemon for smooth backlight control is not 
working for this setup but hopefully the developers that made the daemon will 
add this support! :DI have already asked for that in issue 6.

First, thanks to gpanta...@gmail.com for the accurate information that made me 
wait for 3.2 to reach the repos of Archlinux.

FYI, now, brightness works as expected with nouveau and kernel 3.2.4-1. Soon, 
the same will be true for Debian testing (currently at 3.1.0-1).

Testing this on Precise with linux-image-3.2.0-19.31 (3.2.12) and 
xserver-xorg-video-nouveau-1:0.0.16+git20111201+b5534a1-1build2 and a VPCS11E7E.

As gpanta... says, with acpi_backlight=vendor nv_backlight replaces acpi_video0 
and monitor backlight can be set echoing the value (from 0 to 100), however Fn 
+ F5/F6 does nothing at all (no OSD as well). OSD worked without 
acpi_backlight=vendor, but of course no backlight changes.