YouTube has added a new feature to its TestTube section as of last night, called Active Sharing. With this feature enabled, YouTube will keep track of videos you watch, for both archiving and real-time interaction with other users. If you're watching a video with other Active Sharing-enabled users, you'll be able to see their names with a little green dot next to it to signify they're watching too. Clicking on someone's profile name will show you the last five shows they've watched using the service.
Active Sharing joins the other TestTube projects, Audio Swap [hands-on] and Streams, the latter of which is a souped-up version of this new sharing feature, allowing users to actually chat and interact with each other while viewing videos at the same time. I'd wager to bet Active Sharing is the groundwork for an integrated social bookmarking service being built within YouTube to extend some of these new community features, placing more emphasis on what users are doing at any given time, in a similar fashion to what's been going on over at Digg with some of their visualization projects.