The number one feature I wish HN had is a way to hide a comment family - similar to what Reddit has. This is the way I read Reddit, and it goes much more quickly than scrolling through all of the children once I feel there isn't much more discussion to be had about a particular point. See the image below for explanation (sorry, it can't be a link in the text field of a submission).
http://imgur.com/8hd9q
https://github.com/andrewheins/HN-Comment-Hider