After upgrading to an iPhone 5 and iOS 6, whenever I sync my iPhone or iPad, all music data on my machine is synced. It doesn't matter if I haven't played a song in 2 weeks, all music data is synced every time! In addition, this usually takes about a minute.
So how do you turn this off? Turns out it is easy.
Start iTunes 11
From the Main Menu choose Store --> Turn Off Genius