Every day 268 million people use Google to search for something. The query goes in, the company’s software programs, called spiders, crawl the Web and deliver back the most relevant links. The interaction is so simple—and the hidden calculation behind the results so complex—that it’s no wonder people tend not to notice much about the process. Who bothers to ask the ingredients of a magic formula?

Since Google’s 1998 debut, the search results page—where a home page query is returned with 10 suggested links on the left and multiple advertiser links on the right—has been through seven subtle redesigns. The most recent, in May 2007, saw the addition of images and video in what was dubbed “universal” search. On May 5, Google began rolling out its eighth iteration, which Marissa Mayer, vice-president of search products and user experience, calls “particularly large and particularly important.”

For all of its experiments with maps, books, e-mail, and social networking, Google is still an empire built on search. Ninety-seven percent of the company’s $23.7 billion haul in 2009 came from advertising. While Google doesn’t break out what each of its individual ad products such as AdWords or AdSense generates, multiple people within the company concede that Google is as dependent on the “Sponsored Links” generated by search queries as an oil nation is on its wells.

Since Google’s 1998 debut, the search results page—where a home page query is returned with 10 suggested links on the left and multiple advertiser links on the right—has been through seven subtle redesigns. The most recent, in May 2007, saw the addition of images and video in what was dubbed “universal” search. On May 5, Google began rolling out its eighth iteration, which Marissa Mayer, vice-president of search products and user experience, calls “particularly large and particularly important.”

Given that the shift of a single pixel can impact Google’s profits, why would the company ever mess with the most successful product in the history of the Internet? “The Web is always changing, evolving, and innovating,” says Mayer. “It’s important even for sites that people use every day and are very familiar with, like Google, to update their look.”

It’s not just the look that’s been updated. Microsoft’s Bing, Facebook, and Twitter have made a case for the past few years that Google’s search, based on ranking the overall relevance of a Web page, is outmoded, and that the future lies in an integration of relevance with real-time search. In December, Google conceded the point and announced it would begin indexing the Web in real time to help users organize the cacophony emanating from social media.

Some experts are skeptical of introducing complexity to the results pages. “Advanced search almost never works,” says Jakob Nielsen, principal of the Norman Nielsen Group and co-author of the book Eyetracking Web Usability. “People don’t want to use a search engine. They want to get away from a search engine. That’s the reason the advertising works so well—the search engine is one site they want to get away from so they might go to an advertiser.” In other words, Google has thrived precisely because it hasn’t tried to envelop its users in a full-frills experience.

Still, the competitive landscape is changing. Facebook recently surpassed Google as the most visited Web site in the U.S. Microsoft has unveiled its own plans for Bing, which currently comes in a distant third in the battle for eyeballs but is making a play in searches along topics such as travel and shopping. In March, Bing rolled out a design that adjusts the user interface according to the type of search on four of its verticals. So if it’s clear a user is looking to buy a plane ticket, Bing morphs into a travel engine. “It’s a very radical departure from the dominant paradigm of the link-based system on the Web,” says Stefan Weitz, director of Bing. “For every query, presenting results back with the same user experience doesn’t make sense.