Recently I noticed that only about 56% of my page views are having adsense ads served on them and I am serving a lot of Google Adsense Defaults. Looking at the distribution of page views on my site and where the Google Defaults were being shown was very telling.
The above graph shows the % of times google shows an adsense ad when I serve the google adsense skyscraper code on the 1st, 2nd, 3rd, etc... page a user views on my site. It also shows the % of my page views that fall against each of those buckets. ~25% of my page views come on the first page viewed by a user on my site and 50% of page views come on the 6th and greater pages viewed by my users on my site but on that crucial bucket Google is serving AdSense ads <20% of the time.
It seems Google Adsense simply is uninterested in users who have seen an adsense placement 4 times in a row on my site and not clicked. In this case they roll in your Google Adsense Default selection. That seems pretty fair to me and tallies up with what I have seen in past analysis. What I don't like is that Google only lets me have a static A HREF and IMG banner as my default... that is pants. I would like to fill in with CPM ads from a mix of Burstmedia and Valueclickmedia (my two favourite CPM networks). So what I am going to do now is to swap out the majority of Google impressions for users seeing their 5th page or better but keep a small Google rotation in there so I can monitor if things change. I am going to do that when I get home from my holidays :)
The one thing I would like to change in this market today is for CPM and CPC networks to have API's via which I can reliably pull my earnings and optimize what I am doing. That would revolutionize how I make revenue off my site and I estimate increase my earnings by c. 85% through serving the right ad to the right person at the right time. If anyone knows how I could get this set up I would be really stoked so let me know :)