Any books with a .aa(Audible) or .M4B(iTunes, Audiobook Builder) extension must be managed through the books tab now. Even if you have playlist set up under your music tab and select the playlist to sync it won't sync unless the same playlist is selected under the books tab. Quite lame! It caused me a lot of headaches. When Apple changes something like this, they should have a little pop up come up when you try to sync an audiobook stating this change.
I would like to have the last few hours of my life back. If Jobs is really God, then that shouldn't be a problem.