Brain’s Threaded Comments add a “Reply to this comment” link to every blog comments. When you click the reply link, your comment is placed direct under the comment you replied to. This is great if a reader asks a question. Instead of scrolling down the blog post to see if anyone answered, he can do so by looking at his own comment.
You can see an example of what a threaded reply looks like here.
Having the ability to reply inline in the comments gives the blog a forum like feature and should help to increase comments and interaction level among the blog readership. Give it a try and tell me what you think.