Sometimes when I'm in the app store, I get a .25 to .5 inch bar of noise in the middle of the screen. It only happens once every ten times or so but I'm concerned it is a defect that can only get worse.
I've seen this on my iPhone 5 while in the App store but interestingly I also saw it today on my iPad 3 when in the Maps app. It only happened briefly and I didn't have time to take a photo.
My guess is that this is some sort of rendering bug and will hopefully be fixed by iOS 6.0.1 soon. I'd be surprised if it turns out to be hardware related.