I'm having an issue restoring. I've been stuck on the Apple Logo and progress bar at 5% for 6 hrs. I rebooted the device with HOLD + HOME, and it went back to that unmoving progress bar.
I did this a bit differently than the others in this thread. I downloaded the GM seed the same day as the announcement, on the advice of Lifehacker.com. This rant may have been rendered unnecessary if I had waited for the official release.
It installed handlily, except that all of my music disappeared from the Music app (not the albums or artists, just the song content and titles). FYI - I use iTunes Match. So everything in iOS 6 was working, except the Music app content. I filled the gap with the web version of Google Music, which still doesn't work near as well on the iPhone as Music.
I synced with iTunes via USB a few times. The old content was in there, but in the "other" category (several GB). I managed to get my device back below capacity, and the "other" down ~2 GB, but Music was still unavailable - I just got that large iCloud logo with a static progress bar at 0%, with apparent download activity occuring in the iPhone status bar. No actual music ever became accessible. This problem has also been reported by a few people who waited for the official reelase.
I finally took the dive and went for a Wi-Fi restore, figuring that with iTunes Match "On" I would just end up with iOS 6, my apps & settings, and no music downloaded, since the library was empty, sort of - all songs were indicated, but with no length or titles. Nope - static restore prograss bar for 6 hours.
So here I am - the only backup I can revert to now, besides this morning, is the iTunes backup from April, when I restored my new 4S with my 4 data.
Moving apps and folders is a PITA, even in iTunes. One screen at a time - I can't believe that the Steve Jobs biography had him claiming that iTunes was the "best program on Windows". So far, and this is before I encountered this issue - the opposite is true. Slowest Windows program I have, and I have quite a few. App management in iTunes is a weak port of the iOS method. It's painful to use if you want to move a lot of stuff.
So I restored to April. No non-Apple apps. It restored to "factory"; must have been from when I first got my 4S. Would have been nice to know that was the backup I was working with - how about some screen shots associated with the backup, so you know what you're getting into? I now am looking at a stock iPhone with no 3rd party apps. Time to sync and re-organize 200 apps, and manually re-enter all of the passwords.
Sigh. There's a chance Apple won't publish this reply - a similar one last year didn't make it.