I remember how some forums used to show posts and replies in a threaded Usenet-style. Only the title was visible until clicked on and unread ones could be in bold.
I can't remember any recent forums letting me easily see which replies are new since the last time I viewed the page. I find it hard to believe people wouldn't like this feature. I'd like to see which are the new comments on multiply, slashdot, fark, and so on.
The only thing worse than X Windows: (X Windows) - X