Before this change, only those signed in to Google could use this feature, and had to opt-in to the service. These days, everybody using Google will have their website visit history recorded unless they choose to opt-out of the service. This does raise privacy concerns, and though I could write an entire blog on that, you’ll be able to find many articles on the web that discuss this aspect of using Google’s services.
Google records the results you click on as a part of its mission to deliver the most relevant results to you, and uses the data it collects to “personalise” your results. This means that if you search for a phrase, click on some results but don’t find what you’re looking for, Google takes these websites into account when you rephrase the query and try again, showing you different results than if you had searched for the second phrase first.
It also means that Google learns what you like, so if you search for and click on a certain website a lot, Google will rank that website higher for you, and may show it in a related search when it wouldn’t have done before. Even if you’re signed out, Google keeps information on what you search for in a cookie for 180 days, which is a long time to gather a lot of data on your search habits, especially if you use it every day as I’m sure most frequent internet users do.
Personalized Search reinforces the need to create truely engaging content on websites, as receiving repeat visitors is now more important than it was, and a high bounce rate is more detremental. This is another good point: as well as recording what you like, Google also records what you don’t, and people visiting your site using a certain search phrase and then returning straight away to Google will tell Google that you weren’t that useful to them for that query.
Personalized Search puts power into the hands of your visitors, and lets them almost customise Google’s search results. Although good SEO has always been to put the visitor first, you’ll now be penalised more for not being useful, and rewarded more for delivering content that brings visitors back time and again.