My music collection is kind of eclectic (genre-wise). You never really know what you'll find in there... it might be Bach performed by Emile Autumn (Electronic?) or Angry Skies (Dance Pop?!)... ok so I noticed that the genres on a lot of the music are completely out of sync with reality. They seem to assign the genre label based on the artist rather than the individual song.
So I tried "TuneUp Companion," but this just made it worse. Now I have 57 very specific subgenres ("Electronica Mainstream", "Post-Modern Electronic Pop").. yikes! It made everything more specific, but now my music collection is fragmented along 57 branches in a completely alien non-intuitive way. The "Genius" feature isn't much of a help because it unfortunately ties into the same organization system to help construct it's playlists - "garbage in, garbage out" as they say.
So what's wrong with this? I know iTunes is just trying to leverage existing ways of cataloging music, but the traditional ways of cataloging were born of record companies and promoters, not listeners. Other contemporary software allows multiple tags so that you can capture all the different terms that apply to an item (such as a blog post).
iTunes needs to realize that there's more than one way to organize things in the world.