I don't know if this counts as I went from the 3g to EVO to the Iphone4 (only had the EVO for a couple of weeks). I didn't actually cancel my service, just test drove the EVO to see if it would work for me. Like previous poster loved the notifications bar, and loved the customizations, and the open ability with apps (had an app that would change the default settings, all settings from screen to ringer to what is enabled, depending on time, calendar event, location, etc). Apple will never allow this type of control to happen by a third party software to happen.
I moved back as I liked the screen size and abilities, just couldn't deal with the service issues (4g just isn't ready on this device, which was my reason for switching) and the battery life (that and the wife likes the iPhone better, though was willing to try and compromise).
I did try it and just find the iPhone fits my usage patterns and needs better at the moment, and I can only see it getting better. I need the concurrent voice and data (which was available using 4G, but had really limited service in 4G and I am in an area saturated with it, just signal was very weak, suspect the device) and the Apps are more developed and polished than those available on the Android market (although this will get better, but the same exact app between the two OS yields better results on the iPhone).
These experiences are totally mine and will vary from user to user and depend on each individuals needs and usage patterns.