@BitFlipper: I could see a transparent display as long as the UI elements could be completely opaque. You'd also need two displays sandwiched back to back so that you could also obscure what you are seeing from someone who might be sitting on the other side of the display. That would give you the ability to do some degree of "Does this look right?" without trying to turn the monitor completely around.
Yeah, except for a few scenarios, it's a silly idea. I blame Hollywood. Transparent screens are almost as prevalent in movies as screens that project images onto the actors' faces.