Although it also mentions Yahoo!, an article in the Times yesterday about tracking influenza prevalence using information on Google searches points out how powerful a tool the world's top search engine has become. Google has a public site on flu data.
As Hal Varian points out in a quote, the amazing thing about data on keyword searches is that it can help forecasters track current events far better than extrapolative techniques, which only look backward.
It can't be long before somebody figures out a way to mine Google search data for signs of business cycle inflection points.
