iOS 6 and Xcode 4.5 has a new feature referred to as "Unwind Segue":

  
Unwind segues can allow transitioning to existing instances of scenes in a storyboard

In addition to this brief entry in Xcode 4.5's release notes, UIViewController now seem to have a couple of new methods:

- (BOOL)canPerformUnwindSegueAction:(SEL)action fromViewController:(UIViewController *)fromViewController withSender:(id)sender
- (UIViewController *)viewControllerForUnwindSegueAction:(SEL)action fromViewController:(UIViewController *)fromViewController withSender:(id)sender
- (UIStoryboardSegue *)segueForUnwindingToViewController:(UIViewController *)toViewController fromViewController:(UIViewController *)fromViewController identifier:(NSString *)identifier

How do unwind segues work and what they can be used for?