I agree with the original posters and this is based on my own experience. Vbulletin does seem to have a harder time displaying the appropriate ads. I gave it up and started using SMF as a forum on my site for 4 years now. It is all free and they do have an ad management modification which works pretty good. However, I also have a SMF Gallery attachment which has 5000 images and the Mod does not work in this section. So I have gone in and edited the php files for the gallery and place the ads where I want them to go. Like any forum the struggle is the low CTR. It is hard to keep above 1.25 % on any forum while other parts of my site do much better. However, since 80% of my traffic comes from the SMF forum I am stuck with it. Google is paying so little for clicks now I have not been motivated to look at the forum again and try to increase the CTR