There should be some sort of mention system for threads, so maybe if you put @insertnamehere in a post then they will get a notification saying that you mentioned them or vice versa (you get a notification saying you were mentioned). This would be a bit more useful than watching because that gives you a notification after every post, which can get annoying if it's a super active thread and the replies might not even be to you. I'm not sure how this would be implemented since this forum only seems to use html, but it's a nice concept.