Google is trying its best to deliver personalized search. The official Google blog explains:
We’re constantly trying to improve the quality of your search results. One of the ways we’re tackling this is by personalizing your search experience. After all, you’re the only one who actually knows what you’re really looking for.
We have two main ways of personalizing your Google experience. First, you can customize products and services like the Google Personalized Homepage. Personalizing your homepage gives you the at-a-glance information that you care aboutâ€”such as your latest Gmail messages, news headlines, or to-do listâ€”right at your fingertips, just the way you want it.
Second, we offer automatic personalization through things like personalized search and recommendations. Our goal with these types of technologies is to make your Google search experience better based on what we know about your preferences, without you having to do any extra work.
Today, we’re taking another step toward making personalization more available to you by combining these two into a single signed-in experience. Now, when you’re signed in, you’ll have access to a personalized Googleâ€”one that combines personalized search results and a personalized homepage.
Many of you may have noticed this already for a while — the Google search results showed to you are somewhat based on what you’ve searched and clicked before. This is good because you are delivered the results which is most likely you want based on your search history. That means there’s a totally different and tailored placement in the SERPs for everyone.
Sometimes I like it, sometimes I don’t. Personalized search doesn’t give you the bigger picture. This is even scarier for the SEO guys because it really screw things up. You could be #1 for 5 people, #2 for 10, #8 for 100 and #99 for a million other searchers. So what’s your average rank now?