Yeah performance hit is quite unreal. But I want the aesthetics enough to stick with it, albeit the older devices (iPhone 4, even iPad 2) got a lot of features nerfs. For example, no colouration or blur on the new control centre. Sigh.
I hear on this thread performance has shown to be taken hits on the iPhone 5 too. I call poor optimization and the iOS 7 was rushed for release as a whole.
My other friends who updated their 4s and 5 to iOS 7 have reported high memory use and shortened battery life.