This isn't new for Gmail. I stopped using it a couple of years ago because of this. To be honest though I do believe that ALL these free Email services have bots that scan you stuff to see what you're interests are. Ever notice that you can send someone an Email about a specific item only to have advertisements show up on your free Email page for said item? Yup, seen that one too. Only way to avoid having your "stuff" sniffed is to use PGP encryption, which I do for some stuff I send out.
Welcome to the age of "big brother" my friends!