One of my more popular posts, oddly, is about CapitalOne and Fraud, which is going on nearly 2 years old now. There are a number of comments on the thread, but I noticed something that just started bugging me. When replying, I had no way of creating a nicely formatted reply (threading).
So I went in search of plugins, and discovered that Wordpress 2.7.1 actually supports it natively, you just have to update your themes. I found a great reference here which detailed how to do it, but it seemed to not work, so I went in search of more details. I found that the old comment handling used to be performed using an array, and you’d have to setup the formatting yourself. They now provide a nifty function wp_list_comments that outputs the entire array of comments for you, including all the settings for the reply information.
You can see the new modifications at work here on this post, see the second comment down is indented to reflect a comment to Bill.