Creating a new Smart Playlist or editing an existing playlist with the criteria of "Video Kind" will result in no matches from your iTunes Library because the rule for the Smart Playlist will not be saved.
If you try to edit the Smart Playlist, the "Match the following rule" field will be blank or empty after you click OK. Any additional criteria that is part of the Smart Playlist will remain, but they will produce results from the entire library, not just videos.
Note: Any Smart Playlists that were created prior to updating to iTunes 7.5 will continue to work as long as you don't try to edit the Smart Playlist.
Mac OS X
Use Software Update to update to iTunes 7.6 or later to resolve this issue.