I've been following this issue since the release of iTunes 7... good to see it discussed on MacOSXHints today.
Version 7 of iTunes split the master library up into serveral sections: Music, Movies, Podcasts- for content separation. There are times when it is useful/necessary to see every item in your library in one list.
There are two ways to do so:
1. Create a smart playlist with the following rule:
size is greater than 0MB
2. For mac users: Run the following AppleScript:
tell application "iTunes"
set view of front window to library playlist 1