Apparently (not sure myself, never used it) we used to have a 'mark all content read' link on the New Content page, which we don't any more. Seems like it might be useful - I know there's one in the footer, but it's a bit out of the way (I've had to tell people where it is) and it seems likely people are going to want to use it on the New Content page. Perhaps by content type (forum, blog, pages) depending on what you're looking at, or just globally.

See my solution here: http://www.smartestcomputing.us.com/topic/47507-32x-how-to-add-mark-all-as-read-link-at-the-top/