On newsgroups and forums with similar mechanics, users that want to refer to an earlier comment will quote some of the text and the newsreader will add some marks to the left or indent it or something. After several postings, you end up with long blocks of quoted text at several levels deep.

Weblogs tend to only allow comments at a single level. What if, when reading a posting on a weblog, one could select a paragraph, and then click a Respond button, which would associate the comment with that particular paragraph. Or, better, a fancy inline editor, where one could add text in-between paragraphs. To another reader, the whole text appears as it was originally, but upon selecting a Comments button, the additions are displayed in place.

It might appear something like what happens when you click the Comments button here: