Excitement peaked after Microsoft kicked off a new investment round in the autumn by buying a 1.6 per cent stake in the company. This was closely followed by a $60m investment by Li Ka-shing, the Hong Kong businessman. The deals, which valued Facebook at $15bn, turned Mr Zuckerberg into a billionaire - on paper at least. It also increased the pressure on Facebook to make money from its fast-growing audience - an endeavour that has yielded mixed results.
Mr Zuckerberg this month apologised for mistakes made in the rollout of a controversial new advertising technology called Beacon, which broadcasts messages about purchases made on outside websites to a Facebook user's friends.
Facebook offered a way to opt out of the service after thousands of users complained that it was an unwelcome invasion of privacy.
The struggle over Beacon is emblematic of the broader challenge faced by Facebook as it attempts to reconcile the competing desires of three separate but important groups: the users whose social connections power the site; the developers whose applications keep people engaged once they are there; and the advertisers that Facebook relies on to make money.
"Facebook has these three constituent groups and it's a really difficult balancing act, especially when you are trying to be innovative," says Jeremiah Owyang, an analyst at Forrester Research.
Users have been frustrated by Facebook's missteps around privacy, and developers by its frequent updates to the software toolkit that they rely on to build features for the site.
"Developers are frustrated because the platform continues to change," says Mr Owyang. "There are never-ending tweaks."
The company tries to announce platform changes in advance, in order to avoid unpleasant surprises, but frequent changes can be frustrating because they force developers to make tweaks of their own.
Further friction may be inevitable as Facebook and its competitors experiment with ways to attract developers and make money without alienating users.
"We are in an early stage in trying to monetise social media," says Jeremy Liew of Lightspeed Venture Partners, a venture capital group that is an investor in RockYou, one of the leading makers of Facebook applications. Speaking of Facebook's trouble with Beacon, Mr Liew says, "there are bound to be mistakes made" as social networks experiment with new advertising models.
"It's not a Facebook issue, it's an industry issue," he says.
Still, with Facebook's pace of growth, it has emerged at the forefront of the social networking trend, and all eyes are likely to be on Mr Zuckerberg and his team as they attempt to negotiate an increasingly complex business environment.
Mr Liew says Facebook's rapid response to the outcry over Beacon is a positive sign that Facebook remains focused on users even as it seeks to develop its revenue model.
"Facebook got a bunch of feedback about Beacon, and they changed it. If you can make changes in a period of weeks you are not going to get stuck. It's a stumble, not a fall," he says.
While users may be willing to overlook the occasional gaffe, Mr Owyang at Forrester believes that advertisers may prove less forgiving.
"Marketers are much more particular in how their money is being spent," he says. "They are less likely to give Facebook the benefit of the doubt in the long run."
Striking the right balance is bound to take time.
"In five to 10 years, I can't imagine a future where there isn't a vibrant ad-driven business in social networking. If you asked me is it six to 12 or 18 months, I couldn't tell you. It's going to take some period of years for a standard to emerge," says Mr Liew.
