Qt apps have been flooding the OVi Store these days. We just stumbled on a Qt powered QML Youtube player. Well its as smooth as all QML apps. It is a pretty decent youtube player for your Symbian S^3 devices. It consists of all the option you would expect in a Youtube player such as featured, most viewed, most recent, Top rated and integrated Youtube search.
Tapping on the top of screen zoom the video while tapping down shows the seek bar with player controls.
Nokia N8 promo running in Youtube player.