I would identify these three main use cases:
A: Very basic functionality, for people who were comfortable with the communication provided by simple listserv lists for the last two decades, and who are ready to take advantage of forums software to take this business out of the (overcrowded) inbox.
D: use for intensive, long, structured discussions, for instance, in the humanities (Dorothea's, see link above). Subcases might be Bruce's ones above, Exploratory or Debating (Problem solving, IMO, is rather "A" obove or "X" below.)
X: Usage where users are trying to extend forum functionality into a direction that might be better accomodated by other types of communcation channels but (for some reason) they don't want to (or may not) adopt these. Examples/subcases include
- users who like to retain their inbox workflow as they did in listserv times
- users who think of more advanced social networking features / communities of practice but do not have blogs, wikis, and the like available yet. (The next use case where all these communication channels coexist and forums plays a very distinct optimized role, is IMO not yet realistic). See #2, #6, #7.
I think we should not waste too much time with trying to conduct serious use case analyses for the forums, because we are not (yet) at the stage of fine-tuning and adjusting to sophisticated special audiences but rather try to accomodate basic usability requirements.
Targeting to single audiences, here, will mainly involve the pre-setting of reasonable defaults. For instance, the default value for expand and collapse could perhaps be "collapsed" for use case D while beng "expanded" for others.
