[MarkMc]

> But when your job is influencing which candy bar people select in the supermarket, you stare into exactly the same informational void

Is that necessarily true? Most supermarkets have a 'loyalty card' program which requires the shopper to provide her name, address and date of birth. The supermarket could sell all their data to Facebook, which would then have the fine-grained information needed to allow the candy-bar company to very effectively target their ads.

It might not even require a loyalty card - the shopper's credit card info or security camera picture might be enough to accurately link her to her Facebook account.