iOS 7 UI is significantly laggier than iOS 6 (I honestly do not understand how 4S users deal with it, its not fantastic even on 5S). Not to mention glitchier.
I have a 4s. While iOS 7 is laggier than iOS 6 when doing things like switching apps using a home key double tap etc., it is a much faster interface. That is, there might be (not too heavy) laginess for a small set of tasks, but iOS 7 unlike iOS 6 can keep up with my natural speed for doing things much better.
I think the key is that iOS 7 is 'slower', but the animations are meant to take less time. Thus swiping back and forth through view hierarchies, changing apps, etc. is all faster because the animations are designed to take less time (and animation delay is an artificially induced latency).
This is because of the keyboard. It's extremely heavy weight in iOS 7 for some reason — it consumes quite a lot of memory when it appears. It's not really acceptable, but that seems to be the cause of the stutters (keyboard appear during an existing animation).
Additionally, there's a very slight user-perception / psychology disconnect because of the conflicting animation speeds. The pulldown is gesture-responsive; pull faster and more firmly, and it pulls down more quickly. But the keyboard popup is automatic, and it triggers a split second after the pulldown gesture, always at full speed. The two animations look off-synch in anything but ideal conditions.
I'm on an iPhone 4 - think the lag would be painful on a 4S, put yourself in my shoes. But mostly I just wanted to comment and upvote because I wasn't sure how many other people had noticed it since upgrading iOS.
(NB: I know the age of my technology is part of the issue. Bought it in early 2011, had it replaced under warranty after 23 months in 2013, have only just started to feel the problem so hoping it lasts until the 6 is released.)
