I often find it difficult to tell which posts are new when I load the main HN front page, and I end up spending significant time and mental effort re-parsing the same headlines. This problem is compounded by the fact that my session often expires before I finish reading page 2 or 3 and try to go to the next page, making me reload the front page again and work my way back, by which point I have to scan all the headlines again so I don't miss any stories.
It would be nice if either story headlines I haven't been shown yet could be highlighted, or ones that have recently moved onto that results page could be highlighted, so I can tell at a glance which stories I might not have seen yet.