Great question, and as a side note, one thing I've noticed in SCoPE discussions is that participants often emerge as facilitators and feel comfortable bringing elements that get buried in long windy threads into a new fresh space. It's fantastic.
The audience in discussions like this is often invisible. We have evidence that there are many (many!) people reading along through our "guest" access to SCoPE. Then there's the RSS option which is extra invisible! Sometimes there are conversations springing up elsewhere that refer back to a seminar in SCoPE that give us clues of a more widespread audience. Here's an example from the Knowing Knowledge seminar.