Unlike other BT solutions, Google's program will allow users to edit ad categories and other information via the feature called Ads Preferences Manager.
"Google said that it planned to segment users along 20 categories and nearly 600 subcategories, and would not create categories for certain “sensitive” interests, including race, religion, sexual orientation or certain types of financial or health concerns."
The users will be assigned to these segments based on the content of the pages they visit.