So 3m makes a product which they have dubbed, plainly enough, as the 3m privacy filter. If you follow the link you can see what it does. It is basically some exceptionally small louvres that keep people who are sitting as near as an airplane seat from seeing what you are working on the plane. I can't tell enough how handy this is.
It does attenuate the light a little bit, but it's easy to remove when you are not in a public situation. Just slide it out and you're back to normal. Dirk Hohndel at Intel has one and I've always felt covetous of it, so I ordered one when I got back from Linuxworld in Boston. It took 24 whole hours for Google to have one magically teleported to my desk. So very efficient.