The following was submitted to me via email, and it's an interesting tidbit. I'm sure everyone knows that you can play MP3's in the Finder's column view mode, but did you know that the volume was keyboard controllable and has a "super loud" mode? Here's the email...
I was listening to an MP3 in column preview mode and wanted to select it and some others using the keyboard. So I hit the shift and up arrow keys and the volume started to change! Playing around with it, the up and down arrows adjust the volume, but the shift and up arrow can make the volume even louder (think Spinal Tap's "11"). It appears that the quality starts to suffer using the shift key. Using the up or down arrow alone will return things to the normal scale.
I knew that the arrow keys would control the volume, but I had never thought to try a shifted arrow key. Since this is QuickTime at work, the same trick should work for movies or any other files that QuickTime controls.