I have a 4s and it works fine. Just the general issues that you must free up other major memory hogs if you want good performance on it (ie if I have tumblr in the background, it will be jittery at times).
You may not be noticing it because its serviceable but try an iPhone 5 and you'll see how it's less smooth.
Or if you downgrade back to ios6 you will notice a difference in smoothness immediately.