I have a 2015 Lenovo X1 Carbon, onto which I've installed Ubuntu 14.10 x86-64. The function keys don't work properly. Instead, they behave as if the "Fn" key is pressed all the time. Actually pressing the Fn key makes them behave as if Fn is *not* pressed.
Fn+F1 should toggle mute. Instead, F1 by itself toggles mute.
F1 in a Terminal should open the "Help" window. Instead, Fn+F1 opens "Help".
Alt+F4 should close the current window. Instead, Fn+Alt+F4 closes the current window.
I've since learned that this is new behavior of the Lenovo Thinkpad keyboards. The Fn key now has "lock" functionality, like Caps Lock or Scroll Lock. By default Fn is *on*, and pressing Fn turns it *off*. If you press Fn+Esc, that lights an LED embedded in the Fn key, and now Fn is *off* (and pressing it turns it *on*).