Where is 'Mark All Forums Read' or 'Mark Forum as Read'? I can see 'Unread topics' in Settings so 'Mark As Read' should be added somewhere.
Unread topics shows replies to topics you have visited... whenever you read an unread topic, it'll get automatically marked as read.
Now that you bring this up, I think there should be a way to mark a topic as don't show me this topic anymore. Also an option to stop showing topics older than x days.
I may add the mark as read alternative as well... but it should not be really necessary.