iTunes' behavior when you click the green zoom button is unlike that of other Mac OS X applications. in iTunes, this control toggles between the big main window and the smaller control-only (or control-and-text) window. The same thing happens when you choose "Zoom" from the Window menu. However, if you hold down the option key when clicking the button or choosing the menu item, iTunes will zoom like other apps.
I wanted to be able to toggle from big to small window using the keyboard, so I assigned a keystroke (Command-Option-M in this case) to the Zoom menu item (through Panther's Keyboard & Mouse preference pane). However, when I went to try it out, to my surprise iTunes actually zoomed the window like normal apps. It took me a while to realize it was due to the Option key that was part of the shortcut. I reassigned the shortcut to Command-Shift-M, and now the window toggles correctly. However, Command-Option-Shift-M does not zoom the window, which is annoying.
So when you're assigning keyboard shortcuts to applications, watch out for behavior that changes with modifier keys.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20040208143120318