This is curious. Reminiscent for me of BBC Connector, the chat-around-content application that my team built back in - ooh - 2002?, in an attempt to let BBC web users chat to each other as they browsed web pages. Weblin works in the same way, overlaying avatars onto web pages whereupon users on the same page can chat to each other.
The great thing about this particular idea is that a web page can become a statement hangout: in Weblin's demo video, the page in question is Joi Ito's, which says something about Weblin's creators (maybe Joi has invested, or maybe the Weblins are just fans?). In the BBC's case, we launched the original applicaton with Radio 1, so users could pick the music page of their choice and - hopefully - find other users with similar tastes.
They have leaderboards; what next, I wonder. Quests? Guilds?