I think Google Ad Planner is pretty amazing and chock full of information. But to some webmasters, the information they have is either so accurate it is scary or totally off and worthless.

In a WebmasterWorld thread, Google AdSense representative, AdSenseAdvisor, replied to questions about where they source the data, how to opt out and what to do if the data is off. Let me quote what Google said:

Forum discussion at WebmasterWorld.