Was on reddit today and found a post from someone talking about how they made this service to use with their girlfriend to share music together from both youtube and vimeo players in one place. He had since made some alterations to the site and wanted to know what the public thinks about it, and what they might be able to pull from the service. Read their explanation from the home screen:
synchtube allows you to instantly create public and private rooms where you can watch YouTube and Vimeo music and videos synchronzied with up to 50 people. Everyone views the same video at the exact same time!
Here is the promotional video from the site, teaching you their concept in 60 seconds: