It seems in iOS 6, a drop shadow is automatically added to the navigation bar even when you set a custom background image. I\'m pretty sure this wasn\'t the case with iOS 5
I cannot comment so I'll add my information here.
Perhaps the above suggestions worked in the beta, but it does not seem to be the case now.
self.navigationController.navigationBar.shadowImage = [[UIImage alloc] init];
The above does not work, neither do any of the other similar answers above. I have tried them all.
Clipping to bounds does work but doesn't give the result I want as I'd like other views to hang outside the nav bar.