Google announced some important modifications to the methods used to measure site traffic as reported within its Ad Planner offering.
Since many web professionals rely on multiple media planning tools and rely on analytics tools to measure unique visitors, it's easy to see how reporting discrepancies could occur. To minimize the issue, Google's Ad Planner added a new cookie-based metric to help users cross-check and compare metrics. They have also changed the way they present unique visitors to make it clearer that media buyers are reviewing only estimated numbers of real world users.
Ad Planner has also added country demographics for Australia, Brazil, Japan, and Switzerland, bringing the demographics total to ten countries. In select countries Google has also added a new demographics category, Children in Household, which can be used to research sites.