I use Thunderbird solely as a newsgroup reader where discussions take place. The biggest problem I have is that when I respond to another post in a thread my post shows up in the thread tree as being a response to the original post. As an example let's say there is a thread with 50 posts. I reply to the 27th post in the thread. I do so by selecting that post, clicking on the Followup button and replying directly to comments from that post which are brought in when the message box opens. Instead of appearing in the thread tree under the message I responded to my post is attached at the bottom of the tree. Once in a great while my post will appear under the post I was replying to but that is rare. When others reply to my posts sometimes they appear under my post in the tree but just as often they do not.
Bottom line this behavior can make it difficult to follow long threads with multiple people posting.