To expand the activity streams, YouTube has now added a new feature “RealTime YouTube” that shows a list of friends; who’re currently online, their recent activities and notifies when one of your friends posts comments or rates videos. For example, you can now see all the videos currently watched by your friends. You can disable the real-time sharing and it's also possible to hide the toolbar from YouTube's settings. The features requires an invitation, and if you’ve RealTime toolbar, you can send invitations to 25 of your friends.
Source:→ Google OS