Google claims that it can detect the outbreak of the common flu two weeks earlier than the US Center for Desease Control, based on sudden spikes in relevant search terms -- e.g. flu systems, muscale ache -- that people are using. The set up a site to track this called "Flu Trends." They write
We have found a close relationship between how many people search for flu-related topics and how many people actually have flu symptoms. Of course, not every person who searches for "flu" is actually sick, but a pattern emerges when all the flu-related search queries from each state and region are added together. We compared our query counts with data from a surveillance system managed by the U.S. Centers for Disease Control and Prevention (CDC) and discovered that some search queries tend to be popular exactly when flu season is happening. By counting how often we see these search queries, we can estimate how much flu is circulating in various regions of the United States.
It's pretty clear that while we are learning about the world through Google, google is learning about us. And it does so in real time. While we have to wait for someone to put material out there, Google as access to enormous amounts of raw data as it is being produced and can process it any way it wants, most profitably, one can imagine, for marketing. I guess the pharmaceutical industry is quite interesting in such data. One can imagine that publishing (or witholding) such real time monitoring data is having a real effect in the developing of the underlying phenomena itself.