Not sure if I am a fan of the discussion tab in the Wiki. I realize it is not instant like a forum or chat session, but here are some advantages and challenges that I see in using a wiki collaboration group space.
Advantages:
1. It can be added/edited by others, even if they are not particular to your topic; value in outside opinion
2. It is an ongoing thread that can be looked at from the very beginning; reminds me of going back to original notes or back to the start
3. The opinions of others are extremely valuable, whether you agree or not; interesting to be able to go back and see if changes have occurred over time
Challenges:
1. Not instant feedback like a chat, Skype, Google doc session
2. can be edited or added to by anyone having access to the wiki
3. You would have to keep logging in to check that someone has provided a comment or edited the discussion