I think Hacker News has the right idea - show responses in their own threads, use upvoting to push the best stuff to the top, use downvoting to keep everything

I think Hacker News has the right idea - show responses in their own threads, use upvoting to push the best stuff to the top, use downvoting to keep everything civil (very important), and give people a chance to edit their comment if they see it getting immediate negative feedback.