When you go into a thread there is a bread crumb trail at the top of each thread that can be used to navigate back into each level of the forum.

If you are reading a thead that is long ( a full page ) you have to scroll back to the top to use it. I think it's a great tool but it would be much more user friendly if it was at the bottom of the thread so when you get down to the bottom and you are done reading the trail is right there to for you to access without having to scroll back to the top.