The idea is to simplify navigation, clean up the UI, make things work a lot better, and have a few more needed features. The right-hand menu will be the same as you navigate around the forum, other than on the topic pages. So you can easily switch between My Topics or a forum in the list without having to hit the back button. There's also easy access to your Favorites, which is a nice improvement.
Here's what it's going to look like: