My suggestion is the following: Remove the (x) after each category until you have some consistent postings on the site. Also, I would place the adsense on the category pages in such a way that it looks like they are listings. Maybe add just a little description of each category above the Adsense to help drive the ads more to like what you want. Also, I would move the Post New Ad to the left side of the page so it is more visible.