It would be awesome if HN kept track of new comments on a post. While I can tell which articles I've read on HN because of the a:visited color, I can't tell which comments I've read.

As a solution, I'm imagining updating a timestamp each time I view an article I voted up (to limit the scope of this feature). Then, when I re-visit the comments for that article, any comments with timestamps more recent than my recorded one are emphasized in some way.