It looks like Apple has had great success with iOS 7, which has seen over 200 million installations since it was released. Within 72 hours of its release, iOS 7 overtook iOS 6 as the most-used mobile OS on Apple devices.
Apple noted in its press release that "more than 200 million iOS devices are now running the completely redesigned iOS 7, making it the fastest software upgrade in history." So it looks like Apple struck... gold, with its iOS 7 release. 200 million users downloading and installing any product, not just a mobile OS, is a massive number in itself.