Open several windows, one of them being the Terminal. In the Terminal, type:
sleep 5 && kill `ps aux | grep Dock.app | grep -v grep | awk '{print $2}'`
Now hit the Return key and then press F9, and wait. In five seconds, your Dock will respawn and you will have tiny windows that you can interact with. If anybody actually finds a useful application for this I'd love to hear it.
[robg adds: Yes, I did test this one, and it does work -- sort of. You may have issues working with the windows, especially if they're quite small. I can't think of a valid reason for needing to know this trick, but that doesn't mean it's not worth sharing. One piece of info lacking in the above hint is how to get back to normal, but it's quite easy -- just hit F9 again!]

