Social media specialist Andrew Long was surprised by that number and thought people probably weren't being honest with themselves.
"Either they're underestimating it, they're mistaken or they're lying because maybe their bosses might read it," he said.
Mr Long, the founder of Know Social Media, said some organisations had also banned sites such as Facebook, Twitter and Trade Me.
But others were looking at other ways of curbing how much time people spent on social networking sites, instead of blocking them.
Social media profiles for business were becoming increasingly popular, Mr Long said. "Businesses go where all the people are."
Facebook was launched by Mark Zuckerberg in 2004. Last month, it reached 1 billion users and has been estimated to be worth about US$100 billion.
The company sells the user data to advertisers so they can target specific audiences.
Facebook also offers companies a free way to interact with their customers while promoting themselves. Social branding companies, or in-house experts, were also becoming more common, Mr Long said.
"It started off as a very personal space but now you've got organisations of every kind in there."
Mr Long said he did not see the popularity of Facebook declining.
"People say they don't particularly get any satisfaction from it, but it's seen as a necessary evil in today's world because that's where everyone is."
This year, research found that New Zealanders visited Trade Me more often than Facebook, bucking the world trend of the social media site being the second-most frequented site after Google.
Studies in the United States, United Kingdom and Australia show Facebook and Google with first and second ranking.
But in New Zealand, Facebook took out third place with 73 per cent of the 3055 respondents to a Horizon Research poll. Eighty-one per cent had visited Google and 74.8 per cent had been on Trade Me.
And in September, 350,000 New Zealanders had Twitter accounts.
Q&A: How private is private?
Does Facebook sell user data?
Here's what the firm says: "You have control over how your information is shared. We do not share your personal information with people or services you don't want. We do not give advertisers access to your personal information. We do not and never will sell any of your information to anyone."
So how does it make money?
Facebook makes money by selling advertising space. Most of this advertising is targeted to groups of people and subsets of users. So while it doesn't sell your data to companies, it does use it to allow firms to market to your interests.
How is this done?
Facebook gathers information on its users - such as interests, age, location, job and gender - and uses it to allow firms to target you directly. If a user "likes" designer fashions and specifies their gender, they should expect a related advert to appear on their Facebook page.
How much does Facebook make from advertising?
US$3.2 billion ($3.9 billion) last year - 85 per cent of total revenue.
Is there any way to prevent targeted advertising?
The most obvious thing to do is delete your profile - no profile, no adverts. But as Facebook is a "necessary evil" for many, the best you can do is keep strict privacy settings on your profile.
Is that a permanent defence?
No. Facebook often updates its website, and has in the past changed privacy settings along the way. If you see notes on a new look or new features, check your privacy settings - they may have changed.
Can I find out what personal information Facebook keeps?
All information stored by Facebook - pictures, posts, likes, etc - can be downloaded. Find out more here. This file will not however contain third-party posts about you.
