Update: Many users are reporting that cellular functions and Touch ID are no longer working post update, so we would recommend holding off until further notice. Many who have updated their iPhone 4S, iPhone 5, and iPhone 5s are reporting no problems, so it appears this problem is likely confined to iPhone 6 and 6 Plus.
Update 2: The update has been pulled. Apple has issued a statement to Re/code:
Apple has released iOS 8.0.1 to the public, and it’s rolling out now OTA to all devices capable of running iOS 8. The update’s build number is 12A402, and it packs fixes for a variety of bugs that have plagued users of version 8.0. Most notably, the new version includes a fix for the bug that was keeping HealthKit apps from the App Store. Furthermore, the update addresses a plethora of other problems including an issue with apps accessing photos from the Photo Library, a bug involving 3rd party keyboards, an issue that caused unexpected data usage when receiving SMS and MMS messages, an issue involving ringtones not being restored by iCloud, and more.