I've got Samsung N140 and I am using the latest Kubuntu 10.10 (with all the voRia's extra packages).
The brightness control is working for me now using all kind of ways EXCEPT the hot keys.
If I press Fn-Up/Down, I get the pop-up with the current brightness, but it does not move and the brightness does not change.
After some googling, I found the solution and wanted to share it with you here.
* Create file "/etc/hal/fdi/information/samsung-backlight.fdi" containing (you might need to replace "N140" here with your model)
<?xml version="1.0" encoding="ISO-8859-1"?> <!-- -*- SGML -*- -->
<match key="info.category" string="laptop_panel">
<match key="/org/freedesktop/Hal/devices/computer:system.hardware.vendor" string="SAMSUNG ELECTRONICS CO., LTD.">
<match key="/org/freedesktop/Hal/devices/computer:system.hardware.product" string="N140">
<merge key="laptop_panel.brightness_in_hardware" type="bool">false</merge>
By default, the KDE brightness control code seem to think that all the brightness control is done in hardware and it doesn't need to do anything. The above hint tells it that this is not the case and enables brightness control in software.