One of the features of the OS X Dock is magnification—enable it in the Dock System Preferences panel, and icons in your Dock will magnify as you move your mouse over them. Some people love this effect, some people don’t. I generally fall in the latter group, which is why I’ve always left it disabled. Up until OS X 10.5, those were your magnification choices: on or off.
For as much as I dislike the magnification effect, there are times (especially on a smaller screen) where it would be nice to magnify the icons on a small icon-laden Dock. But to do so would require a trip to System Preferences to toggle the magnification, which makes it not worth doing. In OS X 10.5, though, Apple has added a third mode, which I’ll call “override current settings,” that makes this a simple task.
As you move your mouse over the Dock, hold down Shift and Control. If your magnification was previously disabled, you’ll see icons magnifying as you move. If magnification was enabled, you will no longer see the effect. As soon as you let go of the keys, the Dock’s behavior returns to normal—where normal is the magnification setting as defined in System Preferences.
This is a perfect solution for me; I still have magnification disabled, but for those occasional times when I need it, it’s but a couple of key presses away.