I use Google Ad Manager for showing additional content in one of my sites. It is quite good tool, however there is a significant drawback for it: it has no real handling of CPA and shared revenue based offers. CPM and CPC is everything you get. And sometimes you need CPC ads to compete with CPA offers.
As an example, you have single ad space in the page. You might want to distribute CPM offers through the month evenly, but also show CPA and CPC ads at the same time. Also, depending on current eCPC, you have couple of competing affiliate deals.
Sure, you can solve this problem by entering estimated CPC value for the ad. However, this workaround is not too good: CPC you get from affiliate ads is visitors-dependant often and you might not get same CPC as other sites. Thus initial CPC value is only estimation of real value you will get. You need to update the CPC of these ads continuously. And if you test out various ads for various regions, it is quite a time consuming task.
I wish that Ad manager would release some kind of API that would allow automation of such task. That is posting and changing eCPC values for various ads. This would allow ad revenue maximization for the site by combining all (or almost all) approaches. Is it hard? I do not think so. It would require more dynamical ad rescheduling, but in the end all parties would win. Google Adsense would compete with CPA ads and it would allow Doubleclick integration.
At the mean time, I am planning to take a better look at OpenX project. I think tt does not allow CPA ads either, however I could tweak its PHP code accordingly. I am really interested to see how effective its code is as well. There are some additional benefits of OpenX as well, for example Google-independence, though I am not too concerned with this for a moment.