I can understand what you are saying Robson, but at the same time when you buy banner placement per impressions at least then you know exactly what you are getting.

I guess it depends on the website. Forums generate a lot of page impressions and usually a low CTR because of the nature of the site. The best thing to do as an advertiser is to buy a sample campaign of banner impressions for around $1 then you will be able to estimate how much traffic a decent sized campaign with that website will get you.

There will be horror stories each end of the scale. I am sure that just as many people get stung with bad campaigns paying for banner placement per month. Personally I think the whole concept is very hit and miss.