If you have a ThinkPad running Linux and some sort of hard drive addon, and you patch your kernel and run a Perl script you can program your laptop to recognize patterns of thumping it upside the damn head to call remote support, change your playlist, or download dirty pictures for you.
I’ve used smackbook, which is a virtual desktop switching script for the Mac that uses the motion sensor, and it’s only so-so.
It works OK when you have the laptop on your lap, except that you have to keep it more still than I’d like. If I turn the laptop to show someone something, or shift my weight around, the desktop often changes.
It works even worse, though, on a table. It will always switch desktops when you tap it, but the direction it will go is pretty much random. My theory is that this is caused by the recoil from the little rubber feet that actually contact the table. You tap the Mac one way, but the feet then spring it back the other way. Both are approximately equal in force, so it’s anyone’s guess which way the desktop will rotate.
The smackbook script I used was partially open source, so I did go in and play around with some settings to try to get it to recognize one hit compared to another, but I was not successful. Perhaps someone else has had better luck since then. You could also solve it by always making the desktop rotate in one direction, but that makes it that much worse if you accidentally switch. Now you have to rotate through all your desktops to get back to where you want to be.
I’ve been similarly unimpressed with MacSabre. It does make lightsabery sounds when you move around, but the sounds don’t correlate well to your actions. I really wanted to be able to bring my laptop around in a wide arc and then stop it suddenly to get the “voooom chsshshh” sound, but it pretty much just randomly makes vooming and csshhing sounds independently of how you’re actually moving the computer.