At the moment, (21 Feb 2011) we are using threaded comments on all our pages with comments. This means you can reply to a particular comment and your reply is indented.
I think this can get messy after a while. I am considering changing to FLATCOMMENTS. With flatcomments, you can see the most recent comment on a thread more easily.
You can address your comment specifically to an individual by using the @ symbol.
For example: @michael, I think we should move to flat comments.
What do others think?
If we go to flat comments, we will not be able to easily return to threaded comments.