What if Big Brother is your insurance company who decides to raise your premiums based on eating habits?
The info about your eating habits now becomes a commodity that the store can sell to other businesses or to firms who will crunch the data. Fer instance, it's a little creepy when a woman receives a direct mail ad or free sample for a new feminine hygiene product right around that time of the month...
The potential here is orders of magnitude beyond corporations sharing personal info, say, on your salty food habits or preference in feminine hygiene products. I could care less about that stuff (unless maybe my insurance was cancelled).
The misuse potential lies in the aggragate personality profile taken of you, when millions of factoids about you are crunched in supercomputers (very cheap today).
You've heard of Able Danger, and how "open source" data and supercomputers were used to find Atta and friends.
This methodology can also be turned around and aimed inward at pesky citizens.
"Predictive programs." Might not mean Jack to you today, but it will in a few years.
Insurance companies are in business to make money. If your eating, smoking habits or exercise habits are going to cost them money, they want to know it so they can charge you the appropriate risk premium. On the other hand, if you lead a healthy life they want to be able to attract your business by offering you higher coverage for lower premiums.
It is nothing personal, it is just good business.