Interesting idea. I had a similar idea for HN comments. (@dang: take note.) Impose a delay from the point when a person first makes an HTTP request for a thread, i.e., first reads a thread, before they are allowed to comment in it. This would prevent "real-time" back and forth but it would also prevent knee-jerk comments. Before commenting, a reader would have time to digest the OP and the comments and think about them. A cool-off period. This might produce better comments. It would also prevent people from just jumping into threads that have activity to post mindless commments. It would provide an incentive to dig deeper into HN than only the first page. Digging depper into HN past the front page would give the reader more potential threads she could comment in, should they become active discussions. HN already has a limit on how fast people can comment, i.e., number of comments in a given period.