If you remember a while back, we posted a blog entry where we described that YouTube video playback on an iPad (when running an iPhone/iPod app) was not working correctly. Once playback started, the video was locked in portrait mode, and there was no way to exit the video once playback was finished.
As we described in this same blog entry, the iOS 4.2 update resolves this issue. If you are using YouTube playback on the iPad, be sure to update your iPad to the new iOS 4.2 (available through iTunes). Once your iPad is updated, videos will play back as expected.