I have just received my XPS M1330 preloaded with Ubuntu.  Most of the Fn-key bindings seem to work alright, but I'm having issues with the up/down arrows controlling the monitor brightness.  The keys are indeed changing the brightness but I have an interesting issue.....using 'lshal -m' I can monitor the keybindings, and pressing Fn-(up arrow) ONCE while doing this, I see

13:56:17.581: platform_i8042_i8042_KBD_port_logicaldev_input condition ButtonPressed = brightness-up
13:56:17.585: computer_logicaldev_input_1 condition ButtonPressed = brightness-up
13:56:17.585: computer_logicaldev_input condition ButtonPressed = brightness-up
13:56:17.820: platform_i8042_i8042_KBD_port_logicaldev_input condition ButtonPressed = brightness-up

 and the brightness changes by four steps.  It doesn't seem to be a matter of pressing the key quickly or lightly, and the other Fn keys (eg. battery) work normally.

I can change the monitor brightness in one-step increments only by editing /proc/acpi/video/VID/LCD/brightness manually, but this is annoying.