Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
I restored my iPod Touch 4th Gen this morning and it activated fine, in fact it did it within seconds, the fastest activation of the betas I've seen. Maybe after so many people activated, it's goten weird, but it worked for my at about 1:05 PM PT.
 
I had the same activation problem. I kept hitting the home button at the activation error screen and chose "start over". My phone just accepted the activation a few minutes ago. You will have to be patient if you get this error. Don't downgrade back to 5.1.1.

Your UDID will eventually catch up on Apple's servers. My phone was "bricked" for a few hours.
 
My 4S refused to activate. I restored back to 5.1.1 (power off, unplug, hold home, plug in, restore), then hit upgrade to 6.0 and it worked ok.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.