Google Flu Trends uses aggregated Google search data
to estimate current flu activity
around the world in near real-time.
Google Flu Trends estimate 
United States dataUS-NJ
Since there are historical "reference data" available,
this can help Google engineers to select best keywords for tracking,
and effectively train the algorithm to be optimal based on historical data.
Yes, this could be computationally demanding, but Google has computing resources :)
Similar technique could be used for any other data,
for example stock market prices... Now, most of stock traders
do use historical data of stock prices, but they don't have global context,
including all public news and search info. With that Google (or Bing :)
could create almost perfect stock day-trading tools...
