Microsoft, Yahoo and Google say they are innovating because people's expectations for a search engine are far higher than they were even five years ago. People no longer search for a Web site; now they expect to find a specific piece of information, like the cheapest airfare to Chicago.

"We increasingly find that people think about search the way they think about a public utility," said Susannah Fox of the Pew Internet & American Life Project, which compiled the search data. "When you turn on a tap you expect clean water to come out, and when you do a search you expect good information to come out."

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