When you use the volume controls on a Mac to increase or decrease the sound coming from your speakers, those levels increment in whole steps on a scale from 1 to 10: Press the Up Volume button once, for example and the volume goes up one step out of ten.
But in versions of OS X prior to 10.7, it was possible to adjust the volume in smaller increments: If you held down Shift and Option before pressing the Volume keys on your keyboard, you could adjust the volume in quarter-steps instead of whole ones. For some reason, Apple removed this ability in OS X 10.7. But US reader aGr[j5(6WU noticed that it has returned in 10.7.4 – a change not mentioned in the release notes.
In addition to using this Shift-Option combination to control the volume more finely, you can also use it when you adjust the brightness on your Mac. Press Shift-Option, then press one of the brightness keys on a Mac keyboard and you’ll notice that the brightness changes in quarter-steps. This is nice if you find your display is just a bit too bright or too dim.