I'm not sure how 'useful' it would be, but what if you could overlay this on any web page you wanted, like that asteroids bookmarklet from yesterday. You could have the option to turn it on or off. Kind of an ability to see some real time comments overlay on articles or something. Or just a way to 'hang out' on the HN homepage. Each webpage would have it's own room. It would be like creating an instant chat overlay on the page.

I just feel like this would add a whole new dimension to the web. It's kind of like WoW back when I played. Each region/city has their own chat zone. I spend too much time just browsing random articles, it would be nice to start up some conversations that aren't as formal as comments (not logged, realtime, etc).