A few years ago I decided to sign up for a FB account, and when I finished, FB put up a page that said "Welcome! Here are some people you may know!" And there were pictures of two of my friends and of three people I had never heard of. I immediately deleted the account.

Obviously FB had been keeping track of me when friends mentioned my name, even though I had never given them permission, had never had any kind of transaction with FB.

Now I have an account, but I only use it to check on concerts, etc. I never post anything, and my settings are as conservative as possible.