I recently learned that core data wasn't used internally at apple. That freaked me out, because it made me feel that choosing that technology for a serious project was a mistake, despite the numerous documentation and support apple provides for it.
Actually, I am still hoping that someone will contradict me by providing concrete example of apple software using core data though, because as i stated, i invested a lot in that technology for an important project.
(~/Library/Containers/com.apple.Notes/Data/Notes/NotesV2.storedata is a Core Data SQLite store.)
Largely because it is a complex beast that many don't bother to become familiar with before they use it. Perhaps that is damning enough.
Lots of SQLite and PLISTS prevail, perhaps indicating the domain of data that needs to be stored for your average application.