Add a "most bookmarked" topic sort and/or "# of bookmarks" counter for topics to help identify exemplary topics.
I just bookmarked a topic that I don't have time to check out right now even though I know it will be good... and it got me thinking that being able to see a "# of bookmarks" counter on the topic would be awesome, as would having a topic sort for "most bookmarked" so we can more easily identify and find exemplary topics. I think as a poster, seeing that people bookmarked your topic would also be a nice feeling and so potentially encourage people to submit more bookmark worthy content as well. :)
edit: Ongoing discussion about such a potential feature: https://tildes.net/~tildes/7z8/suggestion_a_way_to_identify_extra_good_topics#comment-26c8