For example, the educators community in Iowa uses #IowaCore for their discussions related to that subject. The group might have a real-time discussion, say, from 5-7 pm on a Tuesday afternoon, with participants hash-tagging their contributions so the thread appears in one column for people who follow that particular hashtag.
Since a single brief tweet can contain a link to a richly textured site, essay, wiki or other content that lends far more depth to a subject, statement or inquiry, the limiting factor of 140 characters can become an asset, streamlining the dialogue in this format to essentials.