Thanks, you bring up a good point.
We actually do have a way of marking all posts in an Forum section as read, using the "Forum Options" button located toward the bottom of the page:
This expands out to look like this:
If you choose "mark all read" it will mark all the threads within that forum as read so it goes from this:
and shows up like this:
We'll see about expanding this in someway to the "Posts you have not read" link, and make it a bit more noticeable and intuitive to use.
Ooh, what does that button do?