I've updated my iPhone 4 and my mac's iTunes - everything syncs fine except for music. I've tried reboots etc to no avail.
I've tried to sync by playlist, artist, album and genre separately and nothing works with the status bar stuck on "Step 4 of 4" on the preparing bar.
Ok guys I've solved it!
In the summary tab of the iPhone deselect everything apart from Automatically sync when this iPhone is connected
I had "Sync only checked songs and videos" checked and by unchecking this I was able to sync my music just as normal