Instead of responding directly to the issues raised by E-Learning Queen, I'll try to explain why I prefer not to use discussion forum myself after having study it intensively 20- years ago. (A shameless plug: my M.Ed thesis was "an ethnographical study of electronic bulletin board system for teacher support" back in the 80s of the last century.)
To explain why I come to this conclusion, let us look at some characteristics of discussion forum first. Please note that these characteristics can be used both positively and negatively - just like most technology, the value is dependent on the utility.
So, what I would recommend today? Surprise! surprise! Online role play simulation! While the media is cold and discussion are permanent, these encourages rational thinking and careful planning. The simulation space reflects the social structure of the persona, not the social structure of a learning institute verse the learners. The professor really has no role in the role play unless s/he is also playing a persona. In that case, s/he is just another persona - and usually, the players do know such persona is actually played by the professor.
Moderating a discussion forum is a tough job - so is moderating a role play. The difference is that moderating a role play is like playing - time just fly. How many times you have when you mark assignments that you will be laughing all the way throughout the marking process? In role play, that is the norm.