The recent scandal around Facebook brought up many discussions on how apparently free things do have a price. But it’s nothing new, really; Seneca warned us about it two thousand years ago.
Our stupidity may be clearly proved by the fact that we hold that “buying” refers only to the objects for which we pay cash, and we regard as free gifts the things for which we spend our very selves. These we should refuse to buy, if we were compelled to give in payment for them our houses or some attractive and profitable estate; but we are eager to attain them at the cost of anxiety, of danger, and of lost honour, personal freedom, and time; so true it is that each man regards nothing as cheaper than himself.
Let us therefore act, in all our plans and conduct, just as we are accustomed to act whenever we approach a huckster who has certain wares for sale; let us see how much we must pay for that which we crave. Very often the things that cost nothing cost us the most heavily; I can show you many objects the quest and acquisition of which have wrested freedom from our hands. We should belong to ourselves, if only these things did not belong to us.
— Seneca. Moral letters to Lucilius. Letter 42: On values.