Like: How we are living the Facebook life
If you stop someone in a British street, chances are about evens that they'll be registered with Facebook - about 30 million out of a population of 60 million are.
If they are an average user, they'll either have been on Facebook today, or they will be tomorrow. Within a month, they'll have posted 90 separate bits of writing, photos or videos to the site, as well as looking at what their 130 friends have done - not to mention the 80 other businesses, charities, events and other groups they've expressed an interest in.
So what is drawing people so strongly to Facebook?
The beguiling offer is to create an online facsimile of your life - and invite you to live it through Facebook in parallel with the physical world (or IRL - in real life - as geeks like to call it).
One of the most powerful appeals of the site is that when you sign up, you will be amazed at how many Friends you have. Of course, Friends don't have to be friends.
Psychologist Prof B.J. Fogg, who studies online behaviour, says Facebook is designed to make interacting effortless: "Humans are naturally lazy and Facebook has made it really easy to connect to people."
Pressing a Facebook "Like" button in response to a comment or brand is about as minimal as it gets: "We are a one-click culture; if we can get satisfaction in one click, we'll do it," he says.
So does Facebook live up to its promise to provide the kind of communications we have IRL?
Well, on the plus side, every time you look at Facebook, what you see has never been seen before or probably ever will be again - because Facebook isn't a website with fixed pages that are called up: it is a database, which creates each page anew on every request, driven by complicated algorithms.
There is a formula that determines which of your friends' updates appear at the top of your page. While you can guess some of what the recipe includes - such as how much you interact with someone - the details are secret.
Any colour, as long as it's blue
Alongside the ever-changing, individualistic Facebook, there is a straitjacket Facebook. Everyone's profile looks basically the same: same design theme (any colour you want as long as it's blue), same question boxes to answer (hometown, languages, employer, religion, people who inspire you etc).
Not for Facebook the teenage-bedroom look of MySpace pages, or even the tastefully customisable templates of Google's Blogger or other platforms where users can build an online shrine to their lives and loves.
But Facebook never wanted that. In founder Mark Zuckerberg's Harvard dorm room, the site only asked its users to upload a picture and a few facts about themselves. It was all about connecting with people you spied across a lecture theatre. It really was a social network, a way of raising your online flag to connect with friends and others you wanted to know.
What defined Facebook users in the early days was their email addresses. If you had a Harvard email, you were probably a genuine student, and could join. If you just had a Yahoo email, too bad, you couldn't. You couldn't even see into the site. It was like a private club with no windows.
Together with its Ivy League pedigree, that gave Facebook a kind of understated respectability. It still comes across as low key, not trying to push itself. There is a sense that instead of being sold something, you are lucky to be allowed in.
All that was very different from the days when anonymity or false identity were the norm online. Messageboards let people play out fantasies of different personae from the spare bedroom. As the famous New Yorker cartoon of two mutts talking to each other behind a keyboard had it: "on the internet, nobody knows you're a dog."
On Facebook, it was different: if people were going to be themselves, the last thing they wanted was to be in contact with someone who wasn't who they claimed to be.
Jaron Lanier is a bona fide geek - a pioneer of virtual reality - who has ideological objections to Facebook. It's not that Facebook users aren't being authentic: rather that the profile they build of themselves is one-dimensional, limited by the tick-boxes and design features Facebook offers.
In his book, You are Not a Gadget, Mr Lanier complains that Facebook epitomizes a trend in which 'content' created by individuals is effectively sold to advertisers in tiny fragments - post by post, picture by picture, user by user.
Dead weight past
In the process, Facebook has tamed personal web creativity, says Mr Lanier, and replaced it with saleable units of personhood: an individual's idea of themselves has been put into the hands of a website.
And Facebook is not psychologically healthy, says Jaron Lanier: now we need never leave the family circle, the old friends, the familiar faces. Our past follows us round on Facebook like a dead weight. It encourages dependence, and offers comfort and support rather than giving us the courage to venture off on our own: we are all 'kidults' now.
Mr Lanier links the popularity of Facebook to a loss of American self-esteem in the world. The Facebook generation will be the first who, according to predictions, won't be better off than their parents, so being someone on Facebook is a kind of a substitute for success in the real world, he says.
Prof Fogg is less pessimistic. He recognises that Facebook keeps people in touch with those they might have lost contact with, but says there's a price to be paid in the reduced time they can devote to their nearest and dearest.
Perhaps so: we found people admitting to spending up to three hours a day on the site, and when we asked about the number of Facebook friends they had, some said they had almost 2,000. One Harvard student replied with great confidence: "more than I have in real life, for sure."
Charles Miller is the producer of Mark Zuckerberg: Inside Facebook, which was shown on BBC Two on Sunday, 4 December.