Most phpBB users really like the “orange thingie” that takes them to the newest post in a topic. (This feature, like many, is only available to users that are logged in.) The image is this one: I like it too. I like it even more since I optimized the query that drives this functionality.
Edit: This post turns out to be wrong. I am leaving it in place, but the code suggestions made here are not effective and in fact will generate SQL errors in certain cases. More details are in the first comment at the end of the post.