Does the iPad 2 or iPhone 4S play HD videos on Youtube?
In the Youtube app video quality is selected automatically based on connection speed, so you will only get HD video if it's available AND you're on WiFi. It doesn't tell you the quality you are getting. On the Youtube HTML5 mobile site m.youtube.com you can select HD manually through a toggle button when it's available and you can do it on 3G but again no indication of the quality other than "HD."