On Mac OS X systems you can adjust the volume in quarter-steps. Press Option-Shift-F11 to reduce the volume by a quarter-step, and Option-Shift-F12 to increase it by a quarter-step. (This is actually really important when you use USB headphones, which tend to be too loud by default.)
You can also adjust the brightness the same way. Press Option-Shift-F1 to decrease the brightness by a quarter-step, or or Option-Shift-F2 to increase it the same amount.
I found this tip on macworld.com.