From Ubuntu 10.04 to 11.10 I can not change my screen brightness. I use an Acer laptop with VGA Intel HD graphic 3000, and I think this is because my laptop (I tried to update BIOS two or three times so I think that make problems)
I must use xbrightness
to fix my problem. You can try to install this package.
It requires some packages like: xutils-dev, libxxf86vm-dev, libxaw7-dev.
After installation finish. You can change the brightness by run for example:
$ xbrightness 50000
You can read more on the man page or home site of xbrightness.
You can use this program while waiting for the bug fixed.