I recently read a NYT article that highlighted how Google search data is being used to predict flu outbreaks at a regional level and in some cases a week to 10 days before they're reported by the CDC. It turns out that a good portion, if not all, of Google's search data is available for anybody to query using Google Insights for Search BETA. You can search on multiple terms and filter by time, geographic region, and category.
For example, look at the worldwide results for cloud computing. Interest has steadily gained in the last 18 months(follow the link and you'll see that surprisingly the peak interest comes from India - the US ranks 6th on the list):
What about social networking sites? Here's the almost exponential rise in popularity of Twitter in the last few months:
Putting it into perspective, look at how Twitter compares to more established sites like MySpace and Facebook:
In the graph above MySpace is the red line, Facebook is the yellow line, and Twitter is the little tiny blue bump in the lower right corner. Three things stand out: MySpace's popularity has peeked and it's on a slow decline, Facebook is red hot, and Twitter has a long way to go before it's as popular as the others.
Given that Google is the de facto search engine for most people it's easy to see how useful – and powerful - this tool can be.