The update is live, but servers appear to be crushed (see my previous article). Hit the link below to learn more about the various fixes.
UPDATE: Maybe hold off on that update, for now. Via [The Verge]
But you shouldn’t hit the install button yet. Soon after the update hit, an abnormally high number of users immediately started reporting that the iOS 8.0.1 update is breaking cellular reception and other features like TouchID. For those affected, “no service” is displayed after the update has been installed, and toggling airplane mode or powering the phone off and on again doesn’t seem to be fixing it.
UPDATE 2: Apple released the following statement through media channels:
We have received reports of an issue with the iOS 8.0.1 update. We are actively investigating these reports and will provide information as quickly as we can. In the meantime we have pulled back the iOS 8.0.1 update.