From a user
"One of the great features of the community is the way discussions and ideas surface to the top of the list when new comments have been added (actually, not so much with Ideas since Ideas don't seem to surface back to the top when comments are added - only when the Moderator changes the status of them). Unfortunately, it's sometimes very difficult to find what that new comment is - especially with popular/multi-threaded ones. It would be great to highlight those comments, somehow (with an icon, bold/normal font or subtle shading), that were recently added to the thread (or added since you last viewed the thread). Right now, you have to look at the date to see what's the latest/most recent."