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.