I hope that the basic iOS UI elements are refreshed a bit, most of them haven't changed since 2007 when the first iPhone came out, but if they dont I can put up with that.
What they really need to change is the iOS notifications system, and app/iOS update system. App updates should come in patches, not full blown downloads. It's not so bad for apps under 20mb, but anything more than that should have the ability to patch as it's mostly going to be data files which should be able to be patched in pretty easily. As for notifications, if they added a decent system for it then I would no longer have a reason to jailbreak.
From a developer POV I hope they add garbage collection into objective-c (i know it's in OSX already, but i want it in iOS) and also scene kit that appeared in lion beta builds that allow for easy 3d rendering.