This movie is actually a fake. It is created by putting a green screen on the powerbook screen and mixing the background image over the green layer of the video.

 The reason I put it here is that a transparent screen like this is completely feasible and may have several advantages. Perhaps this design should become standard.

1) It will save plenty of battery life since the backlight may become obsolete. Any wall or object reflecting the room light can be used instead of internal backlight.

2) The screen can be used in presentations without a projector.

3) Weight and thickness  could be reduced.

Here's the video