Ben Sandofsky noticed this in the release notes for iOS 9. I'd also completely missed this important change and by the number of retweets, so did plenty of others. Never worry about unregistering for notifications again.
While we're on the subject about not worrying about deallocated objects, this framework from Kevin Ballard gives a safer and more elegant syntax for KVO in both Swift and Objective-C. It has automatic unregistering and is thread safe. It's early days, but looks like it's worth checking out.
How would you make Target/Action feel more at home in Swift? Mike Ash has had a go. I wonder if we'll ever see a layer on top of UIKit from Apple which adds these kind of conveniences.
There's been plenty written about guard since it was added to Swift, but in this article Alexei Kzznetsov argues that if your functions are small enough, it shouldn't be needed at all. He takes some example code from the Apple Swift book and refactors it, removing the need for the guard statements along the way.