Graded discucssions are great. I require students to post a minimum of 3 posts/responses over 3 separate days in the module (they cannont bulk post all in one day). I read the posts daily to monitor and occasionally post a question or brief comment to further direct the discussion. It would be great to mark each post as S/U based on my criteria for a substantive post. If a student writes a lousy posts early in the module and gets a U, he knows he has to step it up by the end of the module.
Then at the end of the module I only have to count up the S posts and award a grade without having to re-read the posts. This should be a feature instructors can turn on/off.
3 substantive posts over 3 days = 10 points
3 substantive posts over 2 days = 5 points
3 substantive posts on 1 day = 1 point