If you find problems changing the brightness of your laptop monitor when moving the slider, you can instead adjust screen brightness via the terminal. This tip may not work for all users, but it worked for me on a laptop with integrated Intel graphics card.
Under Ubuntu 11.10/11.04, open the terminal (Ctl+Alt+T) and issue this command to change the brightness of your monitor:
sudo setpci -s 00:02.0 F4.B=60
60 is the brightness percentage, change it to any number from 0 to 99. The problem is that once you reboot your system, your brightness settings is restored to the previous state. However, you can automate the command given above to start automatically at Ubuntu startup by following these steps:
1. Via the terminal, run this command:
sudo crontab -e
2. Insert now this line:
@reboot /home/user/sudo setpci -s 00:02.0 F4.B=60
[Note]: Replace user with your own Ubuntu username.
3. Save your file and close.