Checkout Google Flu Trends
Check out Google Flu Trends, a site at Google.org, which uses Google flu-related searches as a predictor of flu activity, giving them what they estimate as a two-week advantage over the CDC's US Influenza Sentinel Provider Surveillance Network.
The basic explanation of how it works is here. A scientific article on the project, which is to be published by the leading journal (and Mark Logic customer) Nature, is here.
