I usually keep two 20" screens side by side on my desk, so I can code on one and test on the other. I find I can work much faster if I can just make a change in Eclipse, and by the time I turn my head to the other screen, the tests have already run. My new laptop, however, has a 15" screen, which feels a bit cramped when I'm working away from the office. I've been using the fancy Desktop Manager by Richard Wareham, which is a very nice utility to let you keep several virtual desktops, and change between them easily.
Of course, if you're using something like Emacs or Butler, all your keys will be taken already, so you'll need to use some sort of Command-Ctrl-Shift-4 keystroke for the actual desktop switching.
Turns out, the laptop has a built-in motion sensor. Nominally, it's there to protect the internal hard drive. The basic idea is this: If the accelerometer suddenly notices that the gravitational pull of earth is no longer present, the most likely explanation is that the laptop, sensor and all, is currently accelerating at 9.81 m/s� towards said earth. In that case, it will (wisely) try to turn the hard drive off in preparation for impact.
It can, however, also be used in situations not involving lobbing the laptop across the room, fun though that may be.