Google Testing True User-Specified Ads: This is an interesting angle. Google is testing a feature whereby you can swap out the Adsense ads supplied to the page you’re viewing for another, related set, or enter a search term. With this, Google has essentially put a search box on every Adsense page — I bet the click-through rates on ads the user has had some input in delivering are much higher.
Google is testing out a new functionality for AdSense that allows users who are not satisfied with the current ads being served to choose a different set of ads.
To see it in action, go here and look in the left sidebar.