Facebook is celebrating its 500-millionth user, but the social media application has had wide consequences, even for those who have never signed on.
RISE OF THE SOCIAL MEDIA CONSULTANT
Pre-Facebook, the very phrase "social media consultant" would have produced only blank stares from the typical layman.
Now, people like Marcia Conner make their living advising companies on how to use Facebook and other social networking sites.
"The work I do focuses on helping organisations to use social technologies to connect the people in their organisations," says Ms Conner, a partner in the Altimeter Group and author of the forthcoming book The New Social Learning: A Guide to Transforming Organizations Through Social Media.
"They are complementary technologies that can be used to get that same sort of community feeling."
In short, if there's a company with 10,000 people, social networking can be a way to help workers who are doing mutually beneficial things to know of each other's work and to get in touch to share ideas and skills.
But Facebook offered up an even more obvious application - marketing.
As David Kirkpatrick, author of The Facebook Effect: The Inside Story of the Company that is Connecting the World, notes, companies can use the site for advertising and marketing "based on the extremely exact demographic data volunteered by the individual".
Before Facebook, their efforts were based on a mixture of educated guessing and expensive research. Now there is an audience that makes itself a target.
FACEBOOK PRIVACY ROWS
Of course, the number of users and the volume of information they have volunteered is part of what has exposed Facebook to an ongoing assault by privacy activists.
Mark Zuckerberg, Facebook's founder, recently said: "We are building toward a web where the default is social."
But this move towards default sharing of information has earned plenty of criticism.
Facebook made changes to privacy settings at the end of last year. It then provoked a storm in April with plans to share information with third-party sites and promptly had to announce changes.
May's changes brought one simplified privacy control to run alongside a more detailed set of privacy options.
"One of the patterns that has emerged is that Facebook makes a set of changes and walks those back a bit after the backlash," says Kurt Opsahl, senior staff lawyer at the Electronic Frontier Foundation.
"Facebook has been using a mode of asking for forgiveness rather than permission, leading to this progression over the years."
Facebook's defenders are not convinced by the idea that it disrespects privacy, or that the typical user is anxious, says Kirkpatrick.
"Most users are not aware there is a privacy controversy," he says.
He points to the example of his own 18-year-old daughter, who understands as much about privacy controls as she needs to.
"My wife and I cannot see anything. She is using the privacy controls simply not to let her parents see. She couldn't care less about the controversies."
But Mr Opsahl believes Facebook needs to make simpler privacy controls and to accept that default settings should not be changed in the way they have been.
"What users really want is control over their information, a sense of knowing where their information is going and how they can decide what context the information is appearing."
FACEBOOK GROUP AS CAMPAIGNING TOOL
If you start out with a networking space for students, it's not necessarily the most obvious step to see the possibility of a tool for campaigning.
And yet, Facebook has provided an opportunity for a wide variety of groups to attempt to build support for a cause.
At one end of the spectrum it has been used to get Rage Against the Machine to the top of the pop charts in the UK. At the other, it is vital for serious political campaigns.
From the disputed Iranian elections to action against BP over the Gulf of Mexico oil spill, the Facebook group is the first port of call for many.
"Even though it might not have been intended on day one, fairly early on Facebook was a political platform," says Kirkpatrick. "Its creators were interested in that."
FEARS OVER CHILDREN
Within two years of Facebook's launch, the media had begun identifying it as a possible hunting ground for paedophiles.
There have been killers like Peter Chapman, in the UK, who used Facebook - and other sites - to get close to a teenage victim.
Facebook initially said it would not install a panic button on its site, before recently agreeing a new device with the Child Exploitation and Online Protection Centre that would be optional for young users.
Facebook only allows those aged 13 and over to open an account, but it's hard to stop those under that age joining and many parents have concerns even about teenagers being exposed to everything that is on there.
Competitors have responded to these concerns. Mary Kay Hoal runs a for-profit social networking site, Yoursphere, that is aimed at children.
"These sites [like Facebook] were created by and intended for adults. The content is adult.
"There is predatory behaviour, exposure to content, and exposure to people that children should never be exposed to."
FACEBOOK GETTING SO BIG
The sheer size of Facebook is something that could not have been predicted at the beginning, says Kirkpatrick.
"The original mission was just to create a facebook for Harvard University - this book of pictures they used to find cute girls and guys," he notes.
And many of the problems that are identified with Facebook are symptomatic of a company which only has a couple of thousand employees to serve half a billion users.
"The growth itself is an unintended consequence," Kirkpatrick says. "There's no way any company could scale up its systems so quickly. People really do find themselves dependent on it."