I noticed your post yesterday in the thread about company names and I tried out a few conversations with Tjetter. I saved a couple of the URIs:
It's an interesting concept but I wasn't sure what to do at first. What do you say to a person without any context? In each of the conversations the other person inevitably asked if I was male or female. I think it would be easier for people to get involved if there was some starting point, like a question. Get people talking about a topic, even if just to disagree. Something to get them going.
As a more general answer to your question, Chris Wanstrath's talk at RailsConf today/this week is a good read: http://news.ycombinator.com/item?id=596172