The other place I've experienced lots of online conversation is in group forums centered around a particular user group (such Bill Bua's NWP forum). I regularly read and reply to postings on several group forums centered around outdoor activities. These types of social forums, while not tagged as instructional forums, are an unbelievably rich source of interaction and learning. Folks are constantly posting questions seeking advice, trip reports, insights on their experiences, etc.
And of course sites like Facebook are a constant stream of conversation in a forum setting.
In these environments, folks seek out interaction and freely share their thoughts. They have a personal interest and they are engaged.