I'm sure by now you've heard (and possibly read) the New York Times' article in which Target knows which of its customers are pregnant.
You may think it obvious that your health insurance company has certain information about you - more obvious than what Target is doing. However, the information that insurance companies obtain from you goes beyond the obvious methods of data capture. Everyone expects (or should expect) their health insurance company to capture data reported on a claim form (i.e. Procedure and diagnosis codes, data from medical records, medications, etc).
What most people don't realize is that this information goes farther than just simply affecting your premiums. Information obtained from an insurance company, captured in aggregate, is compiled into a database where it is analyzed for certain metrics. If a managed care provider wanted to send mailers out to men in a certain age group about colon cancer and pre-screening options, they will assemble a database of customers fitting the basic criteria - age and sex - but they will also sort through medical information to determine the most at-risk customers for a given disease. When I worked for an insurance company, people would call up all the time and ask why they received a particular piece of literature in the mail regarding heart disease/diabetes/breast cancer/etc, despite the fact they had no claims coded with any of these diagnoses.
We should realize by now that everything has a cost, regardless of the price of something. Take for example, downloading a free application for your smartphone. Usually, that application, if made by an independent developer, will have advertising embedded somewhere in the application. Those ads are usually tailored to the user's experience, as in the case of iAds. How Apple is able to serve relevant ads to it's user base is by aggregating data - the same way that Facebook serves ads on its own site. This is the non-monetary price the consumer pays for a monetarily free application.
Privacy in our modern age has completely changed so much so that we as consumers must forsake a part of our privacy in order to reap the benefits of what is being offered. Despite the fact that Facebook offers little in the way of privacy, it doesn't stop millions of people from using the service every day. To think that the retail world is (or should be) any different is just naive.