I bought a new aluminum Apple Keyboard a few days ago, and found the media keys (F7, F8 and F9) very useful for controlling iTunes. Then I discovered after putting a DVD into my Mac Pro that the media keys stop controlling iTunes and control DVD Player instead. Handy to use the keyboard instead of fiddling with a mouse, especially if you have a wireless keyboard!
Not sure if this is documented, but I haven't heard about it before.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20070815105420736