I just added a new threaded comments feature. Now you can reply to an individual comment as well instead just the entire post. This should allow sub-topics to be expanded and followed with greater ease. Two things to keep in mind are:
1. new comments might not always be at the bottom of the page anymore
2. if you want to reply to the original post then the form at the bottom is what you are looking for.
3. you can only reply to a comment; you can not reply to the reply. this should prevent things from getting too far off topic.