The new update is reportedly killing cell reception and Touch ID
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.
Rene Ritchie posted a fix on iMore.
Apple has issued a support document with instructions on how to downgrade to iOS 8.0 and says a fix is coming in a few days.