As you know I've been living in ID3 tag hell. You know those mp3's that you got from a friend that don't have an informative file name and the tags are completely empty? Picking through those songs one by one trying to figure the song name or artist out takes a rediculous amount of time. Of course you don't want to get rid of the songs, but you don't want to slowly figure each song out either.
Well, there is a solution!
Have you ever heard of acoustic matching? Basically all music files have an audio fingerprint. This fingerprint can then be used to identify your songs. BrainzMusic maintains a database of a huge amount of audio files. Included in this database along with the fingerprints are ID3 tags. So those unruly mp3's without tags are no longer a problem. The database won't work on 100% of your music files, but it is fairly robust and will be able to tackle most of what you throw at it.
The Mac client, iEatBrains, integrates with iTunes which is awesome. Simply load up iTunes and iEatBrains, then select the songs in question within iEatBrains. The search takes a second or two for each song. When the searching is complete you can choose from potential matches and update your iTunes library.
This is definitely a nifty tool if you're music tags are in shambles! Best of all... its FREE :)