It's up at the top of the subforum, right next to the "New" button. You see "Mark topics read", then "373 topics", then "page 1 of 8", then buttons so you can jump to a given page. Alternatively, in the main forum page, just above the subforum sections, you see "View unanswered posts • View new posts • View active topics • Mark forums read" and you could do all of the subforums at once.
Everything appears to be working fine, and looking good!
Well, maybe one critique: The forum/site logo could be revamped, but that has nothing to do with functionality, which is flawless so far. I'd be willing to submit an upgrade if I could find the site font.
I do, however, have a small question. On the old boards, when I clicked on a link it would automatically open in a new window. Now things automatically open in the same window. Is that a default that was switched during the changeover?