Since I also use Ning for blogs and forums, I don't use these much on Moodle, though I do use Moodle forums somewhat like an essay question on the test. I set it so a student can't read any other answers until after they post their own response--then they can read and comment on what others' wrote. I like that quite a lot. I just haven't been able to get Diigo to work through the password log on, so I don't have a really good way to comment on their responses.