Comment 26 for bug 313231

This bug affects me too, but I can confirm that Michael's workaround works for me.
I have the same system as Michael (R61, with Intel X3100 graphics).

Before applying Sebastian's workaround, nothing would change the backlight brightness: not the function keys (Fn+Home and Fn+End), not even gnome-power-manager. The backlight brightness did not reduce on battery power, either.

Hitting the function keys would update the on-screen brightness indicator (although there was a very long delay between keypress and update.) However, the actual brightness of my screen was unchanged.

This problem only occurred after upgrading to Intrepid for me.

After applying the workaround, everything works as it should. =)