I ahve just added ITUNESMEDIATYPE as new field in the side panel and called it iTunes Media Type.
I dragged a selection of audio files into mp3 tag as normal, selected them, and typed "Audiobook" into the iTunes Media Type box. I saved the changes and dragged those files into iTunes.
For some reason, they still appear in my music library but they should appear under Books and the separate area for Audiobooks. But they do not.
Why isn't that field working?