I haven't posted a Boing Boing link in a while, but this one was just too cool. I'd try it, but I don't have that much interesting behind my computer.
Transparent screen illusion: set laptop's wallpaper to a photo of the wall behind it
Transparent Screens is a Flickr photoset of laptops whose deptop wallpaper has been set to a digital photo of the walls and windows behind them, so that they appear to have totally transparent displays. The effect is striking. Link (via Boing Boing) (via Waxy)