Now Google has begun using a cookie placed on users' machines to track their search behaviour and offer personalised recommendations, even when they are not logged into a Google account. This will no doubt act as a wake-up call to those concerned about what the company knows about them and how it is used.
"Previously, we only offered Personalized Search for signed-in users, and only when they had Web History enabled on their Google Accounts," said Google's Bryan Horling, Software Engineer and Matthew Kulick, Product Manager in a blog.
"What we're doing today is expanding Personalized Search so that we can provide it to signed-out users as well. This addition enables us to customise search results for you based upon 180 days of search activity linked to an anonymous cookie in your browser."
"For example, since I always search for [recipes] and often click on results from epicurious.com, Google might rank epicurious.com higher on the results page the next time I look for recipes. Other times, when I'm looking for news about Cornell University's sports teams, I search for [big red]. Because I frequently click on www.cornellbigred.com, Google might show me this result first, instead of the Big Red soda company or others," the two added.
Beyond better search results, the technology can also deliver more targeted advertising,
However, Google may already have been doing this, just not offering the benefit of better search recommendations to users.
At one level this is a win-win: fewer bad recommendations and fewer off-target ads.
Privacy advocates, however, see it differently. Google used to require users to sign-in to get personalised recommendations, but now delivers them to anyone who doesn't opt out.
Because recommendations sent to users not signed-in are shared by everyone who uses the PC, they could potentially reveal unintended information about one user to the others.
This is another of those issues that how you respond to it will be determined by whether you trust Google or not.
If you are willing to accept cookies from the sites you visit, then any of site can collect information about you. Google collects more informatation than most, but offer more free utility in return.
Privacy activists, however, see this as just the latest example of Google encroaching on its customers' personal information.
"The key point is that Google is now tracking users of search who have specifically chosen not to log in to a Google account," Marc Rotenberg, executive director of the Electronic Privacy Information Center told the New York Times.
"They are obliterating one of the few remaining privacy safeguards for Google services."
That may be a bit of hand-wringing, however, as major search sites have long saved this kind of data.
Google is now simply being more obvious about it uses information and offering a benefit to the users themselves, albeit whether they've asked for it or not.
Google offers a page that describes the differences between 'signed-in' and 'signed-out' personalised search.