The title. The "mark all forums read" button does nothing when used in a section, it works in categories, and on the index, so no idea why it won't work in the sections.

Also

Why can't we mark things....... Unread??

Sorry but I have to decline, there is actually a phpBB forums mod for this, but for large forums it apparently inserts a ton of tables into the database to do this which could pose a potential problem. I don't think the system was built to support this kind of feature without such a hack