Turns out you don't need that SkyMall privacy screen after all. As YouTube user Brusspup demonstrates, if you have an old LCD monitor lying around you can make your screen virtually invisible to anyone but yourself.
The trick works by removing the polarizing filter from your monitor and inserting the filter into the lens area of a pair of old glasses. To anyone without a pair of the polarized lenses, the screen will appear blank and white, ensuring that no boss/coworker/public transit seat mate can snoop over your shoulder. In some situations polarized sunglasses can work, but only while viewing your monitor at certain angles, so you're better off trying to construct your own pair.
While we can imagine a whole host of unsavory things you might be able to do with this hack, there's no getting around how awesome the demonstration looks.
Warning: Judging by the looks of the video this project may fall into the 'don't try this at home' category. But if you do decide to give it a shot, at the very least, don't use a brand new monitor! This cannot be undone.