I wouldn't go as far as claim they bare a total waste of time but I find them not very effective way to advertise as the receptors are in the vast majority other forum owners concerned to try to make their own place stand out.

That said I think they can help you to point you in the right direction with the reviews, interact with other admins and learn their own experiences and opinions, make deals to help each other out, etc. Overall I have a good impression of Promotion Forums. I even worked as a packer and reviewer in some of them in the past.