I personally have a iPhone 3GS (running 4.0.2 but 4.1 was the same) and I can't help but notice that iOS 4 isn't smooth at times. Often when I open apps it stutters into opening the app and this same type of stutter happens sometimes when I close apps too. Sometimes it stutters when opening folders and the multitasking bar animation isn't always smooth. Furthermore, I find that scrolling in some apps leaves a lot to be desired. I mean none of these issues are game-breaking but it does get irritating. That being said when iPhone does run smoothly iOS 4 is beautiful to look at, which makes it even more frustrating when it doesn't quite run as smooth or as fast and you'd like it to. I've also read forum posts stating that some people are experiencing these types of things on the iPhone 4 which leads me to believe that this isn't a 100% hardware issue (because the iP4 obviously has more horsepower than the 3GS). I am therefore hoping that iOS 4.2 will solve these small but irritating issues (smoothness of animations, overall speed, scrolling and memory management). I'd be interested in your thoughts.