Facebook: the sale of the century? What is clearer is that even without Zuckerberg at their side, Facebook's chief operating officer Sheryl Sandberg, and finance director David Ebersman have an impressive script to read to investors. At the end of March, the site had 901m people using it on a monthly basis, 33pc more than a year earlier. Daily users jumped 41pc to 526m in the same period thanks to the explosive popularity of Apple iPhones, iPads and Android-based phones. Profits, meanwhile, more than tripled over the past three years to $1bn. But as the eagerly awaited flotation approaches, investors are asking whether Facebook can sustain the profits acceleration. There is little doubt that Facebook looks well positioned to benefit as companies shift more of their advertising spend online - forecast to reach $120bn in 2015 from $68bn in 2010, according to technology research firm IDC. The question, say analysts, is how aggressively will those advertising dollars be chased by Zuckerberg, a self-proclaimed hacker whose mission over the past eight years has been to amass users and ensure they stay on the site as long as possible. In its prospectus, Facebook insists that advertising can "enhance the user experience while providing an attractive return for advertisers." The introduction of targeted advertising and products such as sponsored stories has not, so far at least, prompted many users to ditch their accounts. Pachter of Wedbush, one of a handful of financial analysts who have already started producing research on Facebook, is sanguine: "The asset Facebook has is more information on 900m people than any one company ever has. If they are judicious about how they use it, and tailor their advertising to it, they will do well. Although the company admits it will not be able to keep hoovering up users in the way it has since 2004, history suggests that Zuckerberg's focus will remain squarely on building a platform that lasts. Having a horizon divided into years, if not decades, rather than the quarters that Wall Street chops the world into, has its defenders. "You have to look at this on a multi-year basis," says Arvind Bhatia, an analyst at stockbroker Sterne Agee. They've said they want to focus on the user and that is what you should want as an investor. Short-term they may make some decisions that might not be in line, but a lot of people tell me that they want Facebook to be one of the core holdings in their portfolio. The fund managers, who will decide whether to invest the pensions of hundreds of millions of people into Facebook, were given a glimpse of what this means in practice by the company's results for the first three months of the year. Profits dropped 12pc to $205m as the company, which Zuckerberg founded while still a student at Harvard University, hired more employees, built data centres and spent more on marketing. The importance of making users the prize is a view given greater weight by internet shipwrecks such as MySpace that have sunk or others, such as Yahoo, that are threatening to do so. Zuckerberg knows that to grow, and at the very least maintain its army of users, Facebook needs to remain alive and responsive to changes in the way people are communicating online. The most striking, as well as potentially disruptive, change for Facebook over the past 12 months has been the rapid increase in people accessing their accounts from phones rather than PCs. The company has said that people coming to Facebook through mobile will drive their future growth. That Facebook is focused on this was underlined last month when it paid $1bn for Instagram, the tiny company behind an app that allows users to share photos on their smartphones. "If Facebook were being created today it would launch as a mobile app," argues Michael Gartenberg, an analyst at Gartner. Developing it for the PC would be the last on the list. But it is also a development that last week brought the anxieties about whether Facebook can squeeze advertising profits from these users into sharp relief. In its latest update to its prospectus, Facebook warned that the growth of mobile users is far outpacing the "number of ads delivered." Gartenberg says the explanation is a simple one and, for some would-be shareholders, an alarming one: "There's not really any advertising on mobile. They haven't even started yet," he explains. Facebook also faces brutal competition for those advertising revenues from Google, Microsoft and plenty of other companies besides. What Facebook's mobile future looks like will be a key consideration as investors weigh up whether to buy one of the 337.4m shares the company plans to sell for as much as $35 each on Thursday night. Should they go for that much, shareholders will be paying 99 times Facebook's earnings to become an owner - a steeper multiple than 99pc of the companies in the S&P 500 index. "Whichever way you look at the valuation, it will look expensive," says Bhatia of Sterne Agee. I just think that Facebook is so unique that the traditional metrics don't work. That is an opinion that will make some investors feel queasy but, again, it is something they will have to consider this week. Has the company, as one analyst put it, established a big enough moat between itself and future competitors to ensure it is here to stay, or could it vanish in 10 years? Warren Buffett says he does not know what it will look like in a decade, which is why he will not be on the shareholder register. And for every trump card Facebook can play: its user base, the possibility of tapping China's internet users and Zuckerberg's vision, there is a matching list of worries. The power Zuckerberg will wield, concerns over users' privacy and lack of mobile advertising will be near the top of the list. Haverty of GAMCO says he has yet to make up his mind whether to buy. Perhaps having Zuckerberg at the Boston presentation would have helped.