At Facebook, advertising watches you!

A woman browses Facebook on her laptop. Image copyright Getty Images
Image caption Facebook is a glorified billboard, says the Washington Post's Alexandra Petri

If you think you're a Facebook "customer", writes the Washington Post's Alexandra Petri, you're wrong. You're the product.

The real customers are the businesses that purchase targeted ads on Facebook to reach people like you.

"Facebook, at its moneymaking core, is a system for showing ads to people," she writes. "It is holding our entire social lives hostage in order to force our eyeballs onto its advertisers' sponsored posts."

She continues:

Sure, you can also give it money to buy things for your imaginary farms. But mainly it's about the ads. You can't buy friends. But buy eyes? That you can do. Facebook is the billboard, and we are the eyeballs.

On Thursday Facebook announced that it was going to be making even greater efforts to gather data about its users so it could offer more precise advertising for its business clients - including learning about other websites you visit and apps you run, and allowing you to identify which adverts are of interest.

Petri says that users may not be totally honest about what their preferences really are, however, opting for highbrow offerings rather than the stuff that really interests them.

"Consider the difference between your actual Internet Routine and what you would actually dare tell a living soul was your Internet Routine," she writes. "As I like to say, there is not a soul alive whose browser history, if it were made public, would not fill the world at large with shock and horror."

There may, however, be a more pressing danger for advertisers, says Derek Thompson of the Atlantic. Just because an ad is targeted specifically toward your interests doesn't going to mean it's going to be effective.

He cites a new study by the National Bureau of Economic Research that concludes internet advertising has "no measurable short-term benefits".

A user might ignore the advert or block it using easy-to-install software. Or perhaps Facebook is just doing the advertising equivalent of preaching to the choir:

Maybe Facebook has mastered the art of using advertising to convert sales. Or maybe it's mastered the art of finding people who were going to buy certain items anyway and showing them ads after they already made their decision. My bet is that the answer is (a) somewhere in the middle and (b) devilishly hard to accurately measure.

He concludes:

The Internet was supposed to tell us which ads work and which ads don't. Instead, it's flooded consumers' brains with reviews, comments and other information that has diluted the power of advertising. The more we learn about how consumers make decisions, the more we learn we don't know.

So while Facebook could be gathering more and more data, packaging its users' tastes and interests into a product that it offers to advertisers, it may not really matter at all.

While this may be of some concern to billion-dollar companies like Facebook and Google, it's terrifying to media companies who see traditional sources of revenue - print advertising and subscription fees - withering away. If internet advertising isn't the replacement, what is?

"Companies just don't need intermediaries as much as they used to," writes Bloomberg View's Megan McArdle. "They can build their own Web pages, run their own videos on YouTube."

Much has been made about the democratising power of the internet. In the end, however, the biggest boon could be to free and unfettered speech - for corporate giants.