For most of us, the things we post online aren't intended to be preserved for posterity: when we post a joke, laugh at the last episode of Luther or announce that we're drinking X in Y with Z, we don't imagine future generations will read it.
But they might - and not necessarily in the places we might expect. For example, the US Library of Congress has an archive containing all the tweets from 2006 to early 2010, and it's currently archiving more than half a billion tweets per day.
The internet's default setting is to record everything forever. Wouldn't it be great if it wasn't?
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Remembering how to forget
We've all seen the stories of people prosecuted for offensive drunken Tweets or the job offers withdrawn because of social media tomfoolery, and that can cause self-censorship: you don't post your real feelings about X because you don't want it in the public domain, or you don't check in here because you don't want someone else to know where you are, and so on.
But even if you're careful, the things you post could have more impact than you might expect.
How would you feel if your tweets from the pub meant you couldn't get a mortgage?
Sounds unlikely? Writing in Econsultancy, Craig Le Grice describes a "Facebook mortgage." When John wants a mortgage, he gives the bank the details of his various social media feeds - and the bank uses those to see that he stays in and watches TV, cooks his own food and doesn't go to the pub too often.
If on the other hand he'd been tweeting about regular pub sessions and running out of cash, he'd be stuffed. "Imagine making a mutual promise with the bank that the mortgage you wanted would be in reach if you saved X per month, did Y on a regular basis (validated by location based check-ins) and ticked off list Z (using a dedicated app, for example)."
Putting credit in your tweets
Imagine the bank surveilling you and demanding you check in like that.
It's already happening, albeit not with banks just yet. According to research firm Timetric, insurance firms are using Facebook profiles to assess customers and to check if claims are genuine.
They're also using social media to assess potential customers: as The Fraud Report says, "for example, if you 'like' skydiving or bungee jumping it could suggest you're a risk-taker. Or using Foursquare to let people know you're at a bar or nightclub suggests that you drink. It's not even all about what you post either; sometimes it's what others post about you."
Even apparently innocuous information can be surprisingly revealing.
According to research published in the journal PNAS, analysing nothing more than people's Facebook Likes - information that's public by default - produces "surprisingly accurate estimates of Facebook users' race, age, IQ, sexuality, personality, substance use and political views".
The researchers believe that their methods apply not just to Facebook, but to "a wider range of online behaviours".
This stuff is only really possible because everything's being stored, and there's no real reason why it should be: do we really need Facebook updates to last forever, or tweets to hang around for eternity?
Living in the now
Imagine if the web's default setting wasn't to remember, but to forget. Your drunken posts wouldn't outlive your liver, the daft stuff you said wouldn't follow you around forever and your social media profiles couldn't be scanned by strangers.
Teens do, but that's because they're not playing the same game as the rest of us. As we predicted years ago, the generation now coming of age, the generation that's never known a world without social media, is either avoiding the data hoarders altogether or making sure the data they provide can't come back to bite them.
Their photos are self-destructing Snapchats, their Facebook profiles are overwhelmingly set to friends-only, and according to the Pew American Life & Internet project nearly six out of ten teens rely on inside jokes or "cloak their messages in some way" to ensure that only a very small number of people know what they're talking about.
Perhaps the rest of us should follow suit.