Facebook's new iOS app has been completely rebuilt in Objective-C, which has both pros and cons. The decision will make the app much faster, as we've already seen, and it makes the app more responsive and smoother overall. On the downside, it will mean that Facebook will be slower on updates, because rather than just changing the HTML5 on the website, which would be instantaneous, it will have to push an update through the App Store, which brings the approval delay.
Still, it should make for a better overall experience. There are conspiracy theories that Facebook has done this in exchange for the "deep integration" it is getting in iOS 6, but it may just be that the changes are necessary to take full advantage of the integration. And, it already looks like Facebook may be working towards the same thing on Android.