That's my favorite too. I've gotten into the habit of following discussions by using the Recent Comments page, since it has been so hard to follow what's new with the threaded commenting system, and having new comments highlighted is going to make it much easier to follow the flow of the discussion in context.

There's one issue that I noticed with that feature - viewing an individual comment gets counted as viewing the whole post. So when I click on a comment in Recent Comments, and then click "View the original post" to see the rest of the discussion, there aren't any green outlines so I don't have an easy way to tell which of the other comments are new. I wonder if it could be set up so that viewing an individual comment doesn't count as viewing the post.