Apple's iOS 7 has been available to the public for exactly one month. In that time, about 73% of all iOS users have updated their iPhones, iPads and iPods to Apple's new operating system, amounting to a little more than 250 million devices.
Mobile analytics company Mixpanel has been tracking iOS 7 adoption (https://mixpanel.com/trends/#report/ios_7/from_date:-32,to_date:0) with a graph widget since it launched on September 18. It took iOS 7 three days to pass iOS 6 as the most used version of the operating system and adoption has been steadily tracking up since then. As of Friday, October 18, iOS 6 is on less than a quarter of iOS devices (about 23%) while 3.65% are using iOS version older than iOS 6.
Note: Mixpanel's widget updates in near real time so precise figures are difficult to nail down.
(http://readwrite.com/files/mixpanel_ios7_adoption_oct13.jpg) Source: Mixpanel
The iOS 7 rollout hasn't been all roses for users. Consumers with older iPhones and iPads (http://news.softpedia.com/news/iOS-7-on-iPhone-4-Is-Unusable-Customers-Say-385141.shtml) have reported that iOS 7 has caused excessive battery (http://news.softpedia.com/news/iOS-7-on-iPhone-4-Is-Unusable-Customers-Say-385141.shtml) drain, slow apps that are crash prone (http://allthingsd.com/20131011/apps-on-iphone-5s-crashing-at-twice-the-rate-as-on-iphone-5-iphone-5c/) and and iMessage bug (http://readwrite.com/2013/10/02/apple-promises-fix-to-ios-7-imessage-bug#awesm=~okDBgpKVy7ur6C) that causes messages to not send or arrive late.
Source: After One Month, 73% of iOS Users Have Adopted iOS 7 (http://readwrite.com/2013/10/18/after-one-month-73-of-ios-users-have-adopted-ios-7)