Not a lot keeps Mark Zuckerberg up at night. When he slips between his — presumably luxury — sheets, rests his head and closes his weary eyes, it's unlikely his sleep will be disturbed by worries over his cable bill or the cost of servicing his car. As his peers toss and turn, fretting over the problems they'll have to face the following morning, the 28 year-old billionaire drifts into a deep, satisfied sleep.

At least that's what you might expect…

However, if you snuck into the Zuckerberg household under the cover of night (assuming you manage to evade the inevitable security) you might find the pyjama'd Zuckerberg in the kitchen; pacing back and forth as he hyperventilates into a brown paper bag, his pan of warm milk bubbling-over on the hob.

What could possibly be troubling him? Well, it's very simple: like every other social network, Zuckerberg's staff have one giant headache, how do they monetize their service before investors start using phrases like "return on investment"? And like every other social network, Zuckerberg's staff have fixed their sights on the one area that may deliver the kind of revenue they need to keep surviving: advertising.

Advertising is nothing new to Facebook, they're currently attempting to settle a multi-million dollar lawsuit that alleges they made use of their users' private data in their 'sponsored stories' advertising feature. Zuckerberg himself has acknowledged their interest in targeted advertising, calling 'personal referrals' the holy grail of advertising.

The interest in the 'personal referral' approach shed new light on Facebook's surprise acquisition of Instagram — Facebook purchased Instagram for $1billion this year despite already owning a similar in-house app — when Instagram's terms of service were updated yesterday, as follows:

Some or all of the Service may be supported by advertising revenue. To help us deliver interesting paid or sponsored content or promotions, you agree that a business or other entity may pay us to display your username, likeness, photos (along with any associated metadata), and/or actions you take, in connection with paid or sponsored content or promotions, without any compensation to you. If you are under the age of eighteen (18), or under any other applicable age of majority, you represent that at least one of your parents or legal guardians has also agreed to this provision (and the use of your name, likeness, username, and/or photos (along with any associated metadata)) on your behalf.

One has to wonder if the purchase of Instagram was made to limit the opt-out possibilities for Facebook's one billion users, which would have been substantially greater had the terms only been applied to Facebook's in-house app. Executives can't have failed to anticipate the response the change would provoke, with many users going so far as to describe it as Instagram's suicide note, and sites like Wired publishing instructions on how to delete your Instagram account.

It's important to understand that Instagram isn't claiming ownership of your intellectual property; they are asserting the right to make use of it, anywhere in the world, for the purposes of advertising third party products, without your permission and without paying you a dime.

As of January 16th 2013, expect to see photographs of the most popular kids at school, used to advertise clubs, bars and shops to the least popular. Expect to see the photographs of your girlfriend sunbathing, plastered over adverts for the local singles-scene. Expect to see photographs of your husband, advertising local bankruptcy services.

As blue_beetle stated in the oft quoted MetaFilter discussion:

If you are not paying for it, you're not the customer; you're the product being sold.

As you lay in bed, worrying over what your friends and family, co-workers and neighbors are being sold using your 'endorsement', spare a thought for Mark Zuckerberg; he'll probably be fast asleep.

Have you deleted your Instagram account as a result of their new terms? Do you trust corporations with your personal data? Let us know in the comments below.