Comments are never good for SEO if we want to emphasize certain keywords in the article's text. They make the percentage count of these words the worse the more comments we have. Of course we can paginate comments but then every page of comments has the same text of an article thus resulting in duplicated, tripled, quadrupled etc. article's text on each comments page. The simple solution would be to show only few (chosen number) of comments right below the article so that it wouldn't mess with SEO too much with a link below to "show ALL the comments" on a separate page (with no article's text). A nice addition would be a possibility to choose whether robots indexing our pages should or sholud not index (and follow links ) of "all comments" page. Usability would be better since there would be no need for browsing through tens of comments pages in search of a valuable one and it would make threaded discussions easier to follow.