As with so many things in life, you can't go back

Matt Packham has a Time article about iOS 7:

People don’t like to be told what they can or can’t do. It’s probably genomic. So I sympathized with those who, when I wrote this iOS 7 upgrade pros & cons list last week, were adamant that you could, in fact, round trip it back to iOS 6. I’d listed “iOS 7 is a one-way trip” as a con, a reason to stick with iOS 6 if you weren’t keen on iOS 7′s look, or worried that your older, not-yet-updated apps might throw tantrums.
In order to downgrade to iOS 6, something Apple officially supported during the prerelease iOS 7 beta this summer, you had to download the latest version of iOS 6, plug in your iOS device, switch it to firmware download mode, then click through various iTunes settings to carry off the restore. In order for the process to complete, Apple had to “sign” the firmware, or you’d be left hanging in the wind.
There was apparently a brief period post-iOS 7 launch— a few days only— where Apple hadn’t stopped signing the iOS 6 firmware (thus sporadic claims, technically correct, that you could still downgrade to iOS 6). That serendipitous grace period has now ended, says International Business Times. If you attempt to downgrade to iOS 6 at this point, you’ll get stuck and be forced to reload iOS 7.
Or, as IBT puts it:

If users now try to downgrade from iOS 7 to iOS 6, iTunes will show an error message, indicating that devices running on the public release of iOS 7 are not eligible for that specific firmware build. If you get that error while attempting to downgrade from iOS 7 to iOS 6, you can restore your device back to iOS 7 to get everything running again.

So, I’ll say again: If you’re running iOS 6 and weighing the ups and downs of upgrading to iOS 7, reading about launch bugs as well as all the hip new features, make sure you’re ready to go, because for better or worse, there’s no going back.

Rico says his ladyfriend had issues with how her upgrade went (and will probably, kicking and screaming, have to go to the Genius Bar, a name she hates, to sort it out). This is also why Rico always waits awhile before upgrading system software...