All tested OS were in latest versions (12.04.1 and Mint 13 Mate&XFCE).
Already tried xfce panel aplet for screen brightness,
acpi_backlight=vendor argument in
GRUB_CMDLINE_LINUX_DEFAULT and replacing xfce-power-manager with gnome-power-manager.
Default keyboard shortcut for brightness control should be Fn+F6/F7.
Shortcuts for mute, volume up, down and for disable/enable wifi are working properly.
For now, I'm able to control brightness only by terminal
echo 1 | sudo tee /sys/class/backlight/acpi_video0/brightness.
Just checked Debian Wheezy with Gnome 3 - also works, but I really want to install Xubuntu on this machine.