I didn’t realize how complicated styling threaded comments can be until I watched this video. David Perel published a screencast on From The Couch.com which goes over how to style threaded comments in WordPress complete with source files for the code but more importantly, hand holding to figure out all of the CSS required for good looking threaded comments. While this is a basic tutorial, it was easy for me to get lost between parent comments, sub comments, sub-sub comments, etc, but that is not his fault.

I suggest clicking on the FULL SCREEN mode to see the video clearly.