If you want to hide statusbar or tabbar from a view in a navigation controller (to display it on full screen), set [self setWantsFullScreenLayout:YES], and that view will be presented in fullscreen mode. (e.g like in the Photos app)
To hide the statusbar or tabbar, use viewController.hidesBottomBarWhenPushed = YES; before invoking pushViewController method.

Note
To have transculent-black navigation-/statusbar, use UIBarStyleBlack and set the translucent property to YES, and set tintColor to clearColor.

Source: Stackoverflow.com, iPhoneDevSDK