YouTube is using an invitation system to deploy RealTime, which in some ways parallels the approach Gmail took when that product first launched. Every user to get invited gets another 25 invites of their own, which makes invitations hard to come by at first, but sufficiently accessible to allow the service to grow quickly. In order to invite someone to RealTime, you have to become their friend on YouTube — you can’t just send them an Email to activate it.
Новая функция RealTime на YouTube