The entire article by Stephen Levy is a great read but what I found particularly interesting is the following passage because it describes how every bit of data has potential value:
Keywords and click rates are their bread and butter. "We are trying to understand the mechanisms behind the metrics," says Qing Wu, one of Varian's minions. His specialty is forecasting, so now he predicts patterns of queries based on the season, the climate, international holidays, even the time of day. "We have temperature data, weather data, and queries data, so we can do correlation and statistical modeling," Wu says. The results all feed into Google's backend system, helping advertisers devise more-efficient campaigns.
To track and test their predictions, Wu and his colleagues use dozens of onscreen dashboards that continuously stream information, a sort of Bloomberg terminal for the Googlesphere. Wu checks obsessively to see whether reality is matching the forecasts: "With a dashboard, you can monitor the queries, the amount of money you make, how many advertisers you have, how many keywords they're bidding on, what the rate of return is for each advertiser."
Wu calls Google "the barometer of the world." Indeed, studying the clicks is like looking through a window with a panoramic view of everything. You can see the change of seasons—clicks gravitating toward skiing and heavy clothes in winter, bikinis and sunscreen in summer—and you can track who's up and down in pop culture. Most of us remember news events from television or newspapers; Googlers recall them as spikes in their graphs. "One of the big things a few years ago was the SARS epidemic," Tang says. Wu didn't even have to read the papers to know about the financial meltdown—he saw the jump in people Googling for gold. And since prediction and analysis are so crucial to AdWords, every bit of data, no matter how seemingly trivial, has potential value.