Just in case you want to know why your comment hasn't appeared, this is the explanation.
Comments are only available to people with registered ID, such as Blogger or OpenID. Even though there's no real enforcement of true identities on the internet, anonymity turns otherwise normal people into offensive trolls.
Comments made more than seven days after the original post will be moderated. This is mostly a spam filter.
Comments should be on-topic to that particular blog post. I've started a discussion about something and you're welcome to join in, as long as you actually join in. Write about that thing. Most of my posts have a narrow focus because blogs aren't dissertations, so it should be quite clear what the post is about. Feel free to ask for clarification if the post is ambiguous.
I'll be sure to point out when this policy changes.