This one's important, and a worthy read.
"The idea of you 'owning' the data about yourself is both emotionally and intellectually appealing. This data, which ranges from the critical (your medical and financial records) to the theoretically trivial (what you buy and search for, and which Web sites you visit) defines, quantifies and describes your preferences, resources, habits and health. It is a proxy for you. It is also what every marketer in the entire commercial universe wants to get their hands on."