Do you involve in post exchange to bring in activities and new users on your forums? How often do you engage in post exchange? Well, I think post exchange is a good way to build users and activities on your forums. However, it is also very time consuming as you will have to post on someone else's forums in a hope to get posts on your forum.
I used to do that but at the moment I don't have a forum. Planing on having one soon. Non the less, the only positive thing that can come out of it is stable activity and pumping those numbers. Other than that, it is a fake activity that can only benefit me if google believes forum is being popular. xD