Facebook achieved three main benefits by embracing native code for its iOS app. Foremost, the app now opens faster, without the lag that many users complained about. Second, scrolling is smoother. Third, photos are uploaded instantly. [Source]
I actually gave Facebook as an example 6 months back when I was asked why Objective-C and not HTML5. Facebook has seen the light now.
I could actually use the app today. Load time was nice and actually there are couple of delighter features. If you scroll down, the status-camera-checkin bar will disappear. If you scroll up, it will appear. Also from the picture viewer, you can swipe up to close to viewer. There are few UX issues in new redesign but perf trumps all of them.