The usb keyboard that I have connected to my Dell E6430 running ubunthu 12.04 with gnome 3 does not open the activites overlay when i press the "windows key" on the usb keyboard.
It works just fine when I use the laptop keyboard.
~$ sudo /lib/udev/keymap -i
To find what the key code was and in both cases (laptop and external keyboard) it is leftmeta.
But when I go and configure keyboard shortcuts the leftmeta on the laptop keyboard shows up as Mod2+Super L and from the external usb keyboard it is Favorites.