Update: YouTube has decided to pull the plug on the RealTime feature. The company wrote in the Help Forum:

We've seen some of you wondering what occurred to the Realtime Toolbar. The Realtime Toolbar was recently retired and is no longer an available feature on YouTube.

We were excited to release and experiment with Realtime and it has inspired us for new features on YouTube in the future. We look forward to introducing many new features in the coming months and are sharing them with you all. Many thanks to those of you who used Realtime and for your feedback to us on this feature- your suggestions and input help the Team shape the site and determine what should be developed to further improve the YouTube community.

(Via)

Original Article: Today YouTube has launched the beta version of YouTube RealTime, which comes in the form of a toolbar that resides in the lower right corner of the page on YouTube.

From this toolbar, users will be able to see which YouTube friends are currently online (much like Facebook) and what they're watching. A history of their recent activities on the site are also able to be viewed as well as real-time notifications when they perform activities like commenting, favoriting, and uploading.

At this point, YouTube is only offering the feature to the first 100 people that say "Yes! Sign me up" in the comments section of this post on the official YouTube Blog. Each of these 100 people will get an invite.

"Please keep in mind that you will need to have friends on YouTube for this to work -- the more you have, the richer the experience, so be sure you accept friend invites and actively manage the list," says Ryan Junee, a Product Manager on the YouTube Team."

Junee encourages those who get the invites to give feedback via the forums or in the same comments section.

YouTube also announced some changes to its home page for signed out users today. More on that here.