Privacy is a currency
Privacy is the core currency of the social web, and like any other type of currency system there’s an exchange rate. In this case, the equation boils down to how much privacy the user is willing to give up in exchange for the features and functionality a site provides. It’s a tricky equation, and the answer varies for every user and for every site.
Most of us give up our location to our phone company in order to receive calls on our mobile.
Most of us give up our buying habits to our supermarket in order to receive a minimal discount through our loyalty cards.
I’m sure that you can think of additional examples?