The virtues of these programs are that they organize postings by subject matter and archive them for easy access. Do not fool yourself into thinking that because the discussion is online, its quality will somehow magically improve. In all likelihood, the truth will be just the opposite. Unless you create the proper incentives and environment, the breadth and depth of conversation will be disappointing. Most important, you must provide reasons for your students to participate.
Students are short on time and are often quite good maximizers of self-interest.
One way to encourage student participation is to participate yourself. Another way to encourage student postings is to consider online participation part of overall classroom participation, which affects the final grade. Of course, such discussions promote general technological literacy, which I believe law schools should more actively promote. More important, online discussions are a form of cost-effective office hours. Instead of explaining a complicated idea to one student who comes into office hours, it is better to explain that idea to the entire class through exchanges on a threaded discussion.