It turns out that tagging and ratings are useful not only for blogs and other web content, but also for music on your iPod (the 30 GB video version), especially when you have over 4000 songs in it. Audio files were probably one of the first to support tagging which was really useful for the user. iPod/iTunes (and many other players) can also use these tags to create dynamic playlists based on given criteria. This makes the tags all the more useful.
I listen to a variety of music, and unless the music is properly tagged, it would be nearly impossible (or atleast too tedious) to locate and listen to the song(s) I want to at a given time. The basic tags like title, artist, album and genre are pretty much a necessity, and identifying songs in their absence would be impossible without actually listening to them. Ratings also serve as a useful filtering criterion.
I have also found the dynamic or smart playlists feature of iTunes/iPod to be particularly useful when it comes to listening to music of a certain variety. I create a set of smart playlists based on different moods, ratings, genres etc and when the music tags are updated, songs automatically get into the appropriate playlist(s). This saves a considerable amount of effort and also keeps my playlists up to date.