Because of the iOS 5 only features we want to add, and also the iOS 5 SDK changes to view controllers that Dan pointed out, we’re going to make Calv 4.3 iOS 5 only. We’re getting rid of support for iOS 4. It’s been long enough since 5 was released and there is no way we’re going to clutter our code with hacks so that the view controllers work correctly on 4 and 5.