Apple told AllThingsD that they no longer support Carrier IQ in iOS 5 and plan to remove it from all their firmwares shortly:
We stopped supporting Carrier IQ with iOS 5 in most of our products and will remove it completely in a future software update. With any diagnostic data sent to Apple, customers must actively opt-in to share this information, and if they do, the data is sent in an anonymous and encrypted form and does not include any personal information. We never recorded keystrokes, messages or any other personal information for diagnostic data and have no plans to ever do so.
Users running iOS 4 and possibly earlier versions report having Carrier IQ on their phones. The file is located at /usr/bin/aw_ice2 on the iPhone.