Ask any member of the self-styled digerati about Mark Zuckerberg and they'll probably tell you that, way back in, like, the Digital Stone Age, he was the equivalent of Jack Dorsey.
At least they might have said that two weeks ago. This Dorsey reference is already, we are sorry to say, horribly out of date. Because, of course, last week was a terrible week for Dorsey and his creation Twitter, which went from achingly super-cool to resoundingly unfashionable almost overnight.
It was largely Stephen Fry's fault. The comedian only managed to get himself stuck in a broken lift between floors high in the Centre Point building. It took the maintenance crew half-an-hour to release him, and while he waited, he passed the time Twittering. An impressive 108,000 of his Twitter followers shared the experience, minute by breathtaking minute.
That alone will have been enough to dismay early adopters - the lonely few who feel duty-bound to inhabit the sector's rather sparsely populated cutting edge. But far worse was the widespread media coverage that the story attracted - because, embedded in explanations about what Twitter actually is (or was), there were name-checks of other famous users.
The likes of Jonathan Ross, Phillip Schofield and Richard Bacon. Oh dear, oh dear. Early adopters and opinion formers are now moving on, leaving Twitter to its horrible fate (probably mass-market popularity). As, indeed, they moved on from Facebook in 2007.
So, it was rather appropriate to hear the Facebook founder Zuckerberg making a terrible admis-sion last week. His baby is now five years old. Yes, five. We know because he sent out an e-mail with a link to his Facebook blog. Unfortunately, we couldn't read it at the office because every time we try to log on to Facebook, it's flagged up as an "IWSS security event" and there are instructions to "contact a network administrator".
This ban at Campaign Towers was imposed a few months ago, when the computers of Facebook users began coming under viral attack - but it must have been an easy decision to make, given the widespread assumption in many companies that employees spend 90 per cent of their time at the office on social networking sites.
And that isn't the only negative vibe that Facebook has to contend with these days. There have been all sorts of rows about the misuse of data, either by Facebook itself as it tries to develop ways to commercialise the site, or by unscrupulous hackers. Then there are the scare stories about parents and teachers and employers attempting to use the site to spy on people.
In comparison, the warm glow coverage seems rather feeble. Like the story about Facebook users helping to find organ donors, thus saving children's lives.
Happily for Facebook, though, the public relations deficit seems absolutely irrelevant to the people that matter - potential users in the 25- to 35-year-old bracket. It has 150 million active users worldwide, with 13 million of those in the UK - and UK activity has more than doubled over the past 12 months.
Nor, according to Greg Grimmer, a partner at Hurrell Moseley Dawson & Grimmer, is that trend likely to flip into reverse in the near future. The social networking space is becoming just like the consumer magazine market in the way that it is segmented by age group.
Grimmer says: "There was a theory that the mass market would, following a suitable time delay, follow the digerati along an evolutionary path taking them from Facebook to Twitter and on to Twine. But it doesn't seem to happen. Bebo users use Bebo until they start finding it childish - but when they move on to Facebook, there will be an overlap period when they use both."
Audience growth, however, doesn't guarantee that Facebook will ever make money - and many observers have been distinctly underwhelmed about its whole approach to this question. For instance, Zuckerberg upset analysts in October 2008, when he insisted that audience growth remains the company's clear priority for the foreseeable future - and he argued that too overtly commercial an approach might alienate this audience. It prompted some in the financial markets to ponder whether Facebook could ever be expected to make a profit.
But, actually, many ad industry observers have been impressed by the slow but steady progress the company has made in this area. It sells banner inventory, naturally, but, for many advertisers, the cutest approach is to set up a fan page for their brand and attempt to drive traffic there. Coca-Cola, Nutella, Liquorice Allsorts and O2, for instance, have produced admired (and successful and award-winning) Facebook campaigns.
Robert Horler, the managing director of Diffiniti, argues that its commercial development, headed in the UK by the European commercial director, Blake Chandlee, and the UK sales director, Stephen Haines, is being deftly handled. He explains: "They're going as quickly as they can and doing it sensibly and in a controlled way. People forget that, in the wider scheme of things, the numbers are still relatively small and it isn't easy to find a way to monetise all the traffic."
And Horler predicts that this will ultimately bear fruit. He concludes: "Facebook has clearly demonstrated that it can add value as an advertising vehicle, delivering engagement and sales. In some campaigns we've seen, it's been the best-performing part of the plan and we've been investing more money year on year. Overall, I'd say Facebook is in pretty good shape."