I think you're not aware of the new changes in their privacy policy and new account management features. They used gmail contacts to send random G+ invitations to people last year. That is how I got invite from G+ from one of my friend who never shared anything on G+ but randomly system sent email to check one of his post to all his friends, post that never existed to begin with.
Google now diggs into G+, Reader, docs, gmail, contacts and calendar data to know more about you. Note that even if you delete google account, analytics will keep on logging data from X IP address and will continue to collect data.
Your google search while you're logged into the system will be based on your G+ circle, your friends activity in Gmail, search and G+. I shared a screenshot in google+ thread you can check out how annoying it is to have search influenced by friends and family.