Brian Solis writes a very compelling blog on commenting on blogs and what is going on in that realm on the PR side. It's a must read.
What's interesting to me on the opposite side as well is that there are bloggers who still don't get the "conversation" part of blogging. For instance if you're going to post a question that engenders comments and that is your goal, then the last thing you want to do at the end is wrap up those comments with a post on how you already knew the "correct" answer to the question and all the other commenters have it wrong.
This is not called conversation. And blogs aren't classrooms with a teacher at the lecturn - soley spouting off from his/her knowledge base with no room for discussion. Let me ammend that by saying good blogs are not classrooms with a teacher at the lecturn.
To really get readers and those comments on your blog you have to be willing to also understand and embrace that it's ok for others to disagree with you and it's ok to have an open discussion on a topic and not make it about being right.
A really good blog is very conversational. And how many of us really enjoy conversations that end with "That's why I'm right." How many of us return to converse with someone who "knows everything?"
It's much more engaging and frankly, more edifying if you're willing to put yourself out there in the midst of the conversation - not always as the leader. And actually it can be a very powerful way to learn new things from other bloggers that you might not otherwise learn.