You might find BigDialog interesting: http://www.bigdialog.org/

I'm sure some level of moderation/facilitation could be achieved with trained volunteers as long as there is better process. Right now, there's little to no process: a lot of people talk about a lot of different things at the same time, signal-to-noise ratio is fairly low, while a lot of really good input gets lost in a sea of responses.

There are quite a few existing group processes that do this. For example:

* Dynamic Facilitation captures the discussion as collections of solutions, problem-statements, data, and concerns: http://bit.ly/Ptas
* AmericaSpeaks' town meetings makes use of a "theme team" that synthesizes input from many small groups: http://bit.ly/WLYH

The key to both is that they are heavily facilitated and follow distinct process models.

Matthew, your comment points to one of the main challenges:

How can we take online participation to scale? And what are the structures and processes required to do so?

I've posted a few initial observations yesterday regarding process quality on the Change.gov forum: http://bit.ly/qJRzE