If you are signed into any of the Google Accounts products, Google will consider you as a single user across all these products and combine the information generated from all these sources to provide a “more intuitive Google experience.”
The current personlized search feature is a good example. Your search results will now not only have information from the web, but also from your Google Plus contacts or your own Google Plus profile.
Google has been talking about its unified search policy for quite some time now, and they will officially launch it on 1 March. By sharing your personal information across Google products they hope to “make search better—figuring out what you really mean when you type in Apple, Jaguar or Pink.”
Along with relevant ads, of course.
“For example, it’s January, but maybe you’re not a gym person, so fitness ads aren’t that useful to you. We can provide reminders that you’re going to be late for a meeting based on your location, your calendar and an understanding of what the traffic is like that day.”
Google will also remember spellings of your friends’ names because you have typed them before.
If you aren’t all that crazy about Google’s plan to make your life better, here is an article from Electronic Frontier Foundation on how you can curtail their data collection to a certain extent by disabling Web History in your Google account. Remember that Google can and will still gather and store your information for their internal purposes.
Here’s what EFF suggests you do: