I used to be able to jump into a big discussion, read dozens of comments, log out, and the next day could go back and read the NEW comments in that discussion. With HN, I can do that for my own comments, but otherwise, I have to jump back into the whole thread and scroll past all the accumulated discussion to find new contributions.

And good newsreaders were also able to selectively skip a comment and everybody replying to it (e.g. if a discussion devolved into a tangent that was less interesting), instead of a whole subject.