From EPIC.org:
Google announced this week a new web tool that may make it possible to detect flu outbreaks before they might otherwise be reported. Google Flu Trends relies on individual search terms, such as “flu symptoms,” provided by Internet users. Google has said that it will only reveal aggregate data, but there are no clear legal or technological privacy safeguards to prevent the disclosure of individual search histories concerning the flu, or related medical concerns, such as “AIDS symptoms,” “ritalin,” or “Paxil.” Privacy and medical groups have urged Google to be more transparent and publish the algorithm on which Flu Trends data is based so that the public can determine whether the privacy safeguards are adequate.
If Google makes the drop in numbers, we will see the strength in the real world that has Google.