I think that sort of indicator is still available. At the top level (the list of forums), the folder next to any forum with unread posts will be yellow instead of white. I think that also works next to threads - in fact I think I even saw a few cases where threads had a "new!" icon at the end of the thread name - but I've been mostly using the Active Topics page to see what threads have new posts in them. If you click on "Active Topics" at the top of the page and then pick "Active Topics" under that, you will get to the list of all threads that have had new posts in the previous seven days. Newest posts are at the top of the list.