I haven't run the numbers thoroughly, but there's a team consensus here that iTunes library management and synchronization questions occupy high slots in the top 10 list of frequent questions to Ask TUAW and our tip line. With multiple machines, iPods/iPhones and massive libraries of media, keeping everything shipshape can be a real challenge.
Past posts have discussed several options for sharing and syncing, including products like Syncopation, myTuneSync, TuneRanger and Mojo -- and one item that keeps showing up in the list is SuperSync, mentioned by Mat here. It may not be the most attractive tool for the job, but reports are that it handles the task with aplomb (though it's a good idea to back up your library first).
SuperSync is discounted 50% today via MacZot, at $14.95 for a pair of licenses (allowing you to sync 2 machines); if library cleanup is on your holiday to-do list, it might be a good last-second purchase. We'll aim for a TUAW Faceoff on the various library sync and management tools early in the new year.