Around midnight UK time, my iPhone 5, along with thousands of other iOS 7-running devices which hadn't updated from their dev betas, randomly crashed. An error message of "could not activate iPhone" appeared, and prompted users to sign in with their iCloud details. Unfortunately this did not solve the issue, with Apple's activation server being "temporarily unavailable."
Connecting to and downloading the latest version of iTunes (11.0.5) and attempting to restore to an earlier back-up, I was urged to turn off "find my iPhone" using iCloud.com. Removing my device from the account and attempting to restore it yet again only prompted me to turn "find my iPhone" off again.
With Apple's beta 6 of iOS 7 seemingly expiring, many were left without a way of restoring their iPhones and iPads to an earlier back-up, but there are workarounds at hand, as our commenter Peeh pointed out, with one such example over at iPhoneHacks.com.
Why Apple didn't automatically update users to the public release of iOS 7 is extremely infuriating, though as some people have pointed out, it's not like they've ever extended that courtesy with previous versions.