Google now lets YouTube users invite their friends to join group video chats and watch videos together via YouTube.com.
Since Google publicly launch its Google+ social network in late June, the Hangouts feature (enabling group video chats that host up to 10 people) has let users simultaneously stream Youtube videos as they video chat with their friends.
Google places a link to Google Hangouts below every video. In the screenshots (below), you can see the Hangouts link within the video's sharing section, to the right of to the social media sharing buttons.
After starting a hangout, you can invite your friends on Google+ to watch the video with you and chat about it face-to-face.
The mother of all social networks, Facebook, recently partnered with VoIP service Skype to introduce a free video calling service for the Facebook platform. In contrast with Google's Hangout feature, Facebook's video chat feature doesn't allow group calls and doesn't let users stream YouTube videos.
Outside of Facebook, Skype offers group video chat for up to 5 people, but it requires a paid membership to access the feature.
Google is slowly integrating its new social network into some of its other services. For example, Google recently announced that public posts on Google+ will now appear below relevant links in Google Search results.