Starting this month Google is initiating "Interest based ads". That means that they put a cookie into your computer and base the ads that they display from previous sites that you have visited. That means that the ads that you see on your computer are no longer based on the key words that you typed in. They are based on your interests and surfing history. They will not display sensitive ads dealing with sexual orientation, porn sites, political views, etc. You can opt out if you choose to. Go to Google for more info. They have high hopes for this to bring in revenue for themselves advertisers and publishers.