POSTS ~ are noticed, so talk about the book in posts. Answer questions about the book in posts, so they are easily spotted and can contribute to the ongoing discussion.
COMMENTS ~ are more hidden, and people must take time to look for them. Make the discussion easy for buddies by putting only the less important stuff in the comments -- maybe short comments on something someone said.
LABELS ~ are helpful, so put "HR" and your name in the labels as we read this book. Or else I will add it later so people who click on "everything we've discussed about HR" (now or years from now) will find our full discussion of House Rules. I have been making the labels uniform, but it saves me time if you do it right at the beginning.