A simple discussion board tip to rotate discussion board moderator duties among your students. If your class relies heavily on discussion, then you can appoint one student each week to take charge of moderate the discussion.
That student can formulate a question, write replies and perhaps do an overall critique of the discussion. Not only does this reduce the amount of moderation from the instructor, but it also gives students a chance to assume increased responsibility and focus more on a particular topic.
Note: If your class does not allow rotation through every student, then consider dividing students into teams and rotating or allowing co-moderators.