If you use a Mac, chances are you regularly adjust the volume using your keyboard's volume keys. They're handy enough, but the volume increment is pretty large. Reader cruud writes in with a new-to-us shortcut for more fine-grained control.
Fine tune volume in OS X by holding down Alt(Option)+Shift then pressing the volume adjuster buttons. Also if you hit the volume down button till it shows the mute sign then hit the mute key it will play very quietly.
I've tested and verified both tips, and both are pretty handy, particularly the smaller increments for volume adjustment. Sure you could just mouse over to the volume in your menu bar, but keyboard shortcut lovers will certainly appreciate it.