Adsense just released a new messages section. Publishers will get messages each month that will help them to optimize their adsense to improve performance. There is no guarantee the tips will increase a publishers earnings, but the tip will be worth looking into by the publisher to see if there could be an increase in performance.
It will be interesting to see if the tips do increase performance in the long run. I have implemented the tip that I received on my account and I will have to track over this month to see if there is an overall increase in ad performance.
Read more on the Adsense blog.