Just to give my experience with my 4s.
It's been using it for 3 days and i feel mainly 2 problems that slow down daily usage. One I think is by design, which is the fade in, fade out animations that waste some annoying seconds. It has lost the immediacy that I was used to.
The other, more to the point of this thread is that I feel lag in the general use of safari and especially when typing (maybe not just in safari). Also somewhat intermittently when going from one app to another I'm getting that "it's not as responsive as it was" feeling...
Update:
For the first time, my iphone crashed. It got stuck on the lock screen by pressing the sleep button after taking a picture. No touch input worked, couldn't turn it off (although the power off slider appeared, I couldn't slide it). After a hard reset (I think) touch input came back, but the screen was flickering, like it had a very low refresh rate...