"Back in 2009, during the swine flu epidemic in the U.S., Google launched Google Flu Trends
(see chart above). The National Institutes of Health found it helped them track outbreaks of the disease. It turns out that when people started to feel feverish and nauseous, they would go to Google to check out their symptoms. While it wasn't a perfect indicator, Google Flu Trends often beat government predictions about flu outbreaks by a week or more."
The article and NPR radio segment "A New Tool For U.S. Intelligence: Google?" goes on to report that Google trends is being used to gather intelligence, understand the mood of a country, and help predict political unrest.