If I use hardware keys to adjust brightness (Fn + F5-"less", Fn + F6-"more") on my notebook Asus F6E, then brightness varies fits and starts. When I change the brightness from the maximum to a minimum following happens: from maximum brightness varies sharply at the minimum, then gradually increases to maximum. Maximum brightness is achieved when the indicator on the screen is at a minimum. If, notwithstanding the provisions of the slider in the leftmost position, further reducing the brightness, it slowly comes to a minimum.
If I twist the brightness using sliders in the "System-> Options-> Power-> Set brightness of the screen", the brightness varies smoothly, without falls. But at least the scale (0%) corresponds to maximum brightness, a maximum of the scale (100%) on the contrary a minimum brightness. The slider in brightness applet for GNOME panel behaves the same way.
In GDM brightness properly regulated, as needed. If I use an old kernel (2.6.27-10) instead of a new (2.6.27-11): the brightness is also regulated properly, as needed.
System: Ubuntu 8.10
I have a ASUS F3JC and have the same problem.
Brightness Fn keys work as described above.
I only want to add that when you plug / unplug the AC Adapter it always reduces the brightness. Also after logging in GDM, brightness is reduced.