It appears that Google may be about to instate a new privacy policy that will allow them to track users across all of Google's properties, including GMail, and allows them to use the information they gather. You will be forced to opt into the new policy.

Google announces privacy changes across products; users can’t opt out

It looks like the wording that they are using is putting a real happy spin on their Big Brother activities.

Do you want Google scanning all of your GMail communications? They may already be doing that and this move is intended to protect their hind end from law suits.