I kind of think that if you have to document something like this, it's too late.
Specific suggestions I have include:
Lift the screen on press of shift or control, the traditional keys for clearing a screensaver (I think there's a bugzilla for this)
If someone is moving the mouse around for a while and hasn't figured out what those arrows mean, maybe display some text? Or something that looks like a clickable button?
I am running gnome-shell-3.9.4 on a mostly F19 system, and what happens is that when you start typing the curtain is automatically lifted. The same happens if you press enter.
Cheers, Debarshi