there's a little "new" button in blue that appears next to a topic when there are new posts, and on the main forum page the icons to the left of the subforums will turn red when something is new.
Yeah, I've got that part, but most forum systems have a "read all new posts" that allows you to see everything new in one page without having to hit each individual forum. It's especially good for slower traffic boards, as you can catch up on all that's new pretty quickly. Was hoping SMF had something similar.