Event.control and friends are inconsistent on different platforms.

Example: the following script will show "Control down" immediately on lctrl keypress in a windows standalone, and will clear the label immediately on lctrl release. However, an OSX standalone won't show anything unless another key or mouse button is pressed together with the modifier (and won't clear the field until it gets another non-modified event). Linux is currently somewhere in between, because we don't know which behavior to match.

-- begin unityscript --
#pragma strict

function OnGUI () {
if (Event.current.shift)
GUI.Label (Rect (10, 10, 500, 30), "Shift down");
else if (Event.current.alt)
GUI.Label (Rect (10, 10, 500, 30), "Alt down");
else if (Event.current.control)
GUI.Label (Rect (10, 10, 500, 30), "Control down");
else if (Event.current.command)
GUI.Label (Rect (10, 10, 500, 30), "Command down");
else if (Event.current.isKey)
GUI.Label (Rect (10, 10, 500, 30), Event.current.character.ToString ());
else
GUI.Label (Rect (10, 10, 500, 30), String.Empty);

-- end unityscript --