I actually kind of regret the year and a half I spent tagging (and verifying by listening to each of) my MP3s. Reason is, I didn't plan the structure well enough. I had this grand plan to have a "matrix organization": playlists organizing my music one way and genre tags organizing it completely differently, giving me two methods of organization for the price of one. Unfortunately, the playlist and genre structure evolved into the same damn thing, so it was a huge duplication of effort.

To contribute, I'll say to consider "mood playlists" or some alternative forms of organization. If you're going through your entire collection, create a few different ways to organize the music in that one effort. You can either do playlists one way and genre tags another way (like I tried), or even copy songs to multiple playlists (which doesn't duplicate the song's hard drive space usage). This could give you, say, a playlist tree by genre then artist, and a mood playlist tree, and a "favorites" playlist tree.

So yeah, think about it, realize the many possibilities, and get it right the first time. Otherwise you'll be like me who may have to spend another six months creating a new organization system because my genre structure is getting tiresome. If only there was a "mood SOUP mode" or something.