When you click on a thread on the main forum page under the "recent" posts section at the bottom, it will take you to the most recent post from that thread. If you're online enough, you can monitor that and really get a crack at seeing every single new post posted…

If you're not online all the time, you will only see the top 10 most recent posts (whch show up as thread links on that main forum page under "recent" posts… when you click on the thread link, it takes to you to that recent post if you wait a second, it anchors to it.

Past that, you really can only look through the forums or use the drop down "new / recent" up above, which should alert you as to what topics are recently commented on.