In 2009, Google published a fascinating paper about predictions based on search data. The company has made use of this data in kinds of ways, such forecasting flu trends and predicting the impact of the Gulf oil spill on Florida tourism.
You can see the forecasted interest for all kinds of things using Google Insights for Search. Own a gardening web site? You might want to know that people are going to be looking for information on planting bulbs in April and October.