Update: iOS 8.0.1 upgraders are reporting problems with Touch ID and cellular connectivity after installing Apple’s update. You should wait before taking the plunge. If you’ve already installed iOS 8.0.1, here’s how to downgrade to iOS 8.
Apple has pulled an iOS 8.0.1 update that fixed problems with HealthKit and various other features after iPhone 6 and 6 Plus users discovered the update broke Touch ID and blocked cellular connectivity.
The iOS 8.0.1 update was also supposed to improve Reachability on the iPhone 6, but it has already been removed while Apple addresses the nest of new bugs it unleashed.