To expand a bit (apologies if this is too verbose, figure it's better to try to be clear than not!):
In a post that is both a reply and has been replied to there are two buttons that help give you context to it's place in the conversation: in the top right there's a curvy arrow with the name of the user you replied to. In the bottom left there is a button that displays the number of posts that have replied. The top right button exposes the parent hierarchy of the current post, the bottom left exposes a single level of children to it.
The bottom left button has a light grey highlight around it, as well as a larger font that I feel gives it more visual prominence than the top right button. I think the danger of pushing people to reading single level replies is that is requires people to jump around the thread to follow a single conversation, but this means that other posts are being skipped in the process.
Maybe it's useful to know which posts have a reply to them, but I think the emphasis should be on the parents of a post rather than it's children - readers will come to those as they read the thread, after all. But if you're jumping into a thread then seeing the immediate context for the latest post is the most important thing, imo.
On that note it would also be useful to view a single level of parents, and then expand for the full history. I've noticed that with longer conversations the history can be long enough to push the current post out of the viewing window.
/re-reads what he's written
Well that was a long way of saying not much. Well, you did ask for it.