An issue I have with forums that handles posts and pages like this is that anyone who gets to be post nr 20, 40 etc is immediately buried. Now, this is just a personal thing I've done a few times, but I've made sure to not post when a thread has say a last post that ends in 19, 39 and so on, because I figure my post will just end up as the 20, 40th (etc) and missed as soon as another one posts.
What I would suggest:
When a thread reaches a new page, there could be a little box above the top post of the page, containing the last 4-5 posts from the previous page. Seems like a very unneeded thing but personally I think it'd be very, very good. Discourage the "last page" avoidance and keep posts visible even if they get an unfortunate position. I mean, if you want a higher chance to be heard you WANT to be post nr 21, 41 and so on.
And if not, make the thread post count count total amount of posts (including OP) and not just replies pweety pwease? :3