Ive been using PMW for several years now for our non-profit website and it has been great!! I find it much easier to work with than some of the newer sites. My only complaint is the postermywall tag line on the bottom unless you pay to remove it.
Allows us to improve the site by collecting anonymous site usage data.
Allows us to show PosterMyWall ads on other websites.
Allows us to show relevant designs to site visitors.