I think the biggest things you'd notice are the missing back button and more apps are rejected depending on what apple decides to allow at the time. I think you'll be waiting for jailbreaks and maybe even paying for things in Cydia so that you can get closer to the experience you had on Android. I came over from iOS (iPod Touch 4G) and I don't regret it. (And yes, you have to pay for pretty much every app over there too) I'd recommend you try out an iPod Touch before going the full commitment and getting the next iPhone on a 2-year agreement, just my 2 cents.
I had a Touch a while back. When I got my first Android Verizon didn't have the iPhone so I really had no choice at the time.
My wife and son both have the 4. I like them except for the size. I really just think it's time for a change.
I really like the third party support too. Mainly the vast amount of available docks, speakers, etc.
We'll see when the 5 comes out. I want to see it in person, handle it to see how it feels, etc.
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