Concern

This is really neat: SmackBook Pro. The short of it is that you can, with a Mac notebook that has a motion sensor, switch between virtual desktops by slapping the side of your notebook.

This does need to be liberated from relying on non-free software, and it would be better if Desktop Manager (which I used to use, but gave up on for a while) worked a bit better on Tiger and x86. But heck, you could use the same mechanism to toggle Expose. Or even make it so if you shake your laptop a bunch, the windows on screen wander a little. It is a great UI — you get feedback on your computer to physical things you do to it. Probably more practical in handheld devices, though.

Also, at some point, someone is going to have to write an etch-a-sketch emulator for OS X.