Andrey Doronichev on the official YouTube blog:
For all you diehard YouTube fans out there who can’t get enough YouTube on your mobile, we’ve got some great news: starting today, you can download the official YouTube app for iPhone and iPod touch from the App Store, bringing you more of the videos you love and more ways to share them with the people you care about.
The new app features access to more videos, a new channel guide, predictive search suggestions, sharing on Google+, Facebook and text message and more. It’s a free download.
This is a replacement for the “built-in” app included with iOS 5, which will go away with the next major iOS release.