Google's Secret Weapon

Google can cross-reference each user's query patterns and result preferences with those of similar profiles. That allows it to serve up future results that each user finds more relevant to her individual needs. Still, while the appearance is one of narrow personal attention, it is actually the vast amount of large-scale data that allows Google to be so precise.

The same goes for the style and presentation of search results, says Arnold. When Google understands that a user is likely a medical professional instead of an enthusiast, the search engine can skew result pages in the direction of more serious medical journals instead of blogs, for example.

The entire process is automated: Google guesses the type of the user by statistically corroborating behavior among different population groups, and delivers results based on user preferences indicated by the data.

Is More Data Better?

Not everyone agrees about the importance of Google's data edge. While conceding that more data is usually better, Doug Leeds, senior vice president of products at Ask.com, maintains that its importance tends to diminish dramatically beyond a certain threshold. And all the major search players are already at the point where they have crossed that threshold, Leeds believes.

"More data does ultimately give you better results, but it doesn't help that much once you get beyond that point of statistical significance," Leeds says. "Once you reach that level, additional data mainly just reinforces the results you would have reached anyway."