Just like anything else, stay out of the discussions you don't like and participate in the ones you do. If there's a subject you feel should be discussed, start up a discussion. Either that, or you have the option to start your own POD site.
I totally agree with Jenny, everybody registers here and put their work up and then they are talking about nothing but selling. I go a lot to restaurants and people there don't want to do nothing but eat. horrible:)
I personally enjoy looking at images posted in the forum and find a lot of the other discussions pretty boring. It doesn't seem that difficult to identify an image thread and avoid it if you don't like them. Besides, they seem to generate a lot of views and comments for images I post in them so someone is enjoying them.