One of the things I noticed when I installed Xubuntu 12.10 was the lack of brightness on the monitor. Initially thought it was a problem with the graphics drivers but then I discovered that there was a plugin that lets you increase the brightness of the monitor easily.

To install the plugin just open a terminal window and type:

sudo apt-get install xfce4-power-manager-plugins
After installation give a right-click of the right mouse button on the top panel. After choosing the panel> add new items and search for "Brightness Plugin".