This script will allow you to merge the track contents of two or more playlists or delete any number of playlists at once, including Smart, Genius, and Playlist Folder playlists. The merge feature will prevent the same tracks that may appear in different source playlists from being duplicated and has an option to delete original playlists. The delete feature only deletes the playlist; tracks, of course, remain in the library.
Very handy when assigned a keyboard shortcut.
Also see Delete Empty Playlists.
OS X 10.6 or later only. Previous universal version (without the merge feature) available at the link below in the "Info" section.
About to merge two selected playlists to a single existing playlist. The tracks in the two selected playlists will be copied to the target playlist.
Perform search-and-replace on text in your choice of tags
Change the settings of hidden iTunes preferences
Export artwork of selected tracks to parent or specified folder
Delete characters from the beginning or ending of selected tracks' name, artist, album, comments, composer, or show tags
Export files of tracks in two or more playlists to single folder
App displays files in iTunes Media folder which are not in iTunes library