After a few hours of OS4 usage,can say that its pretty cool.The folder option is handy and keeps all your apps neat and tidy.The ibooks is ok,but how many ppl read books nowadays.Other than that ,the rest is pretty same,just that on 3GS,there is a tiny bit of lag compared to the 3.1.3 version.It is quite noticeable.

Oh i just realized that with OS 4,when you press and hold the ! button,it will show you the inverted ! too..The same goes for a few more other buttons