The biggest by a long shot for me is UICollectionView. The open source drop-in replacement to get it working on sub iOS 6 is a fantastic effort, but it's not there yet (animation).
One thing that I find incredibly fast and easy to do on iOS6 vs. iOS5 is implementing post-to-Facebook (and Weibo) using the new Social Framework. In iOS5, you would have to
- Register your app on Facebook
- Integrate the FB SDK (or maybe a third-party wrapper)
- Implement various authentication/delegates/callbacks
- Test that you did all of these things correctly
This might not sound like a big deal but it does save some time.
Not that I disagree that iOS 5 was obsolete the second that iOS 6 was released (the numbers agree with us), but...
if (NSClassFromString(@"UICollectionView")) // or something that makes a lot more sense, but that came to mind immediately
{
// facebook stuff
}
// Twitter.framework stuff
Aside from UICollectionView and AutoLayout that were mentioned, there is much easier way to localize the app (one storyboard and many "strings" files, more ways to easily customize UI elements, and a few ARC things (no more manually managing dispatch queues, zeroing weak references, etc.)
