I own two iPhone 4's. My wife has an iPhone 4 as well. My daughters use our iPod Touch 4g. All are running the latest public build of iOS 5. We also have a Kindle Fire.
Here's what I can say about the iPhones/iPod:
* Apps never ever crash.
* Apple designed apps especially never ever crash (*cough* Safari *cough*).
* They never lockup or crash system-wide.
* They never "brick" during a routine update, which would force techie users to Google how to boot the device to DFU mode, and would force non-techie users to call Apple support (thankfully this never ever happens).
* I have never, ever, not once, clicked on the wrong thing.
* I have never, ever ran into a bad UI design.
* I have never, ever played with a demo iOS device in the store that was not working properly, even though hundreds of people have been using and abusing it before me.
Compared to my family's perfect iOS devices, the Kindle Fire is complete crap! (Yes this is sarcasm.)