Fred Wilson discusses the effort behind good user comments and conversations:

But if the author of the news story, or opinion piece, or blog post, tends to the comments, replies to the good ones, signals the bad ones, chastises the loudmouth bullies, and generally runs the comment threads like a serious discussion group, a serious discussion will result.

It's an issue for the news industry because tending to comment threads is not part of a journalist's traditional job. But I would argue that it is now and they ought to get busy doing it. For one, the journalists that do it and do it well will be better read. And they'll be better informed. They'll get tips in the comment threads. They'll get constructive criticism that will help them do their job better. And they'll get leads on new stories before others will.

I'll add this: The tipping point for comments is when users stop talking to the author of a piece and start conversing intelligently with each other. Reaching this commenting utopia requires an inclusive mindset from the original author/writer/poster. You have to value discourse, not just top-down pontification.