Here's a quick tip about a keyboard shortcut new to Leopard (OS X 10.5) that I didn't know about.

If you normally have Dock magnification turned off, holding Control and Shift while moving the mouse along it will temporarily turn on magnification. As soon as you let go of the keys, the magnification will turn back off again.

The Dock will magnify based on the settings in the Dock section of System Preferences, which you can only change when magnification is turned on. As a result you'll have to turn it on, choose your preferred magnification level and turn it back off again.

The keyboard shortcut works the other way round too. If you normally have magnification on, holding Control and Shift will temporarily turn it off.

I'm not sure how useful this feature is, but it's interesting none the less.