iOS 8 is now installed on 63 per cent of active iPhones, iPads and iPod Touch devices that can run the latest, greatest mobile operating system from Apple. While it took a while for iOS 8 to gain traction (mostly because of user apprehension that some bugs existed and needed to be fixed), speed of adoption of iOS 8 is rising quite quickly.
iOS 8 was released together with the new iPhone 6 and iPhone 6 plus in September. Apple has been quick to issue patches and updates (see post below) and has already seeded iOS 8.2 to developers for release in the near future.
Source: Macrumors.com