Today (11/19/2012) I spoke with a planner with the City of Wilmington, NC. She told me that Wilmington had the owner occupancy regulation for quite some time (was not sure how many years ago this was put into effect). A property owner--Broadus Hill--was cited for a violation and decided to go to court. You can read the opinion here:
Currently Wilmington allows accessory units up to 1,200 square feet but not more than 35% of the primary structure.
I think the nub of the case in Wilmington was that the owner occupancy requirement was trying to effect ownership rather than zoning.
Here in Raleigh we should allow individual neighborhoods/subdivisions to choose whether or not they want to allow accessory units.