When using the volume control function keys on an Apple laptop, there's a limited amount of control over the volume -- each key press moves the volume by one entire unit in the onscreen bezel. However, by pressing Shift and Option along with the volume key you want to use, you can break up each large step in the volume control bezel into four parts, instead of having to use the menu bar item or System Preferences for fine-grained control.
[robg adds: I don't have 10.4 with me on the road this week, but a friend tested it for me and said it did not work. Hence, I've marked this hint as 10.5 only. If that turns out to be wrong, please let me know. Someone else with an external third-party keyboard said it didn't work for him in 10.5 -- so this hint may also require a laptop Mac and built-in keyboard. If someone can test using an Apple external on a desktop and/or laptop, please post your results in the comments. (Being on the road this week, the macosxhints.com test lab has been reduced to a MacBook Pro running 10.5 with the built-in keyboard.)]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20080112002445560