I am on iOS5 right now. I only know one other person with it, but iMessage is great so far. Delivery is instant, same with receiving. Same goes with typing notifications (like when someone is replying to you). It's been buttery smooth so far.
I like the notification system better on iOS 5. I love the drop down notifications like Android (but better) and I like the lockscreen notifications. I like how the notifications pop up while you are doing something else, it is much better than what is currently on iOS. Much much better.
Although there is no LED notification (iPhone 4 doesn't have that, the iPhone 5 may), I like it better overall. BB notifications are still top notch.
