I should have checked there first, more fool me. Howard Rheingold’s Syllabus for Virtual Communities and Social Networks at Stanford. As you would expect, it contains some of the references that have come up in my posts and in the comments received, and a whole lot more besides. I am told that Hillery’s definitions of community alone make the delving worth the while.
My thanks to Howard and to Stephen for getting me worked up in the first place.