The company said on a webpage that as of Sunday 47 percent of Apple mobile devices are running iOS 8 after it was released about two and a half weeks ago. That is much lower adoption rate than that of the previous version, iOS 7, which was running on about 70 percent of device about two and a half weeks after its release, according to an estimate by Mixpanel.

http://bits.blogs.nytimes.com/2014/10/07/after-a-buggy-start-apples-ios-8-is-adopted-more-slowly-by-customers/?_php=true&_type=blogs&_r=0