I often get curious about what's inside a Mac OS X application. Fortunately, it's easy to find out just what's inside most of them because of the way Mac OS X applications are stored on the file system. What presents itself as a single object in the Finder is often, in fact, a directory on the file system. This packaging gives the user a single item to deal with (in most cases), while that item contains resources, icons, executables (potentially for multiple platforms - it was this way in the OpenStep days), etc.
While playing with iTunes 4.1, I noticed that the preferences window takes on a behavior that is expected in Jaguar - where in preference style windows (windows with a toolbar that switches between panes), selecting an icon to go to a different view causes that icon to be highlighted. Part of me wondered if there was a special library/framework included to give it this functionality, so I opened up the iTunes Package and peeked inside.
I didn't find any extra libraries of frameworks, but I did find a lot of icon files. Of particular interest - a WMA (Windows Media Audio) icon. I then tried dragging a WMA file into iTunes (OS X version), but it didn't play.
Curious that it's there...