when there's a topic you haven't read, it will look like a colored notebook beside it. if you have read it, it will have like a white top sheet on it. when you hit mark topics read, they will have that white sheet thing, for whatever reason you want to mark all topics read. mark all forums read will do the same, except to all the different forums for people who maybe stay on the main forums page, and just check each individual forum when a new post has been made.
the only way i would see this actually coming in handy is if you've read the ones you want to read, and the others you don't care for you've ignored, you can hit all topics read. when you do this, the new topics you may want to read will stand out more, and you won't need to deal with having them mixed in with the topics you don't care about... :/ hope i made sense.
the only thing i don't understand is why some of the books are red, and some of them are blue. =*(
