John Burbank, CEO of Nielsen Online, says "social networking has become a fundamental part of the global online experience... (and) will continue to alter... the global online landscape... (as well as) the consumer experience at large... "

According to the report, the world's most popular social network is visited monthly by three in every 10 people online across the nine markets in which Nielsen tracks social networking use. Other key findings include:

• One in every 11 minutes online globally is accounted for by social network and blogging sites.
• The biggest increase in visitors during 2008 to "Member Community" Web sites globally came from the 35-49 year old age group
• Mobile, in social networking, is up 249% in the UK and 156% in the US over last year; 2 million people in the UK, and 10.6 million in the US

The story is consistent across the world, ‘Member Communities' have taken a foothold in every major market from 50% of the online population in Switzerland and Germany to 80% in Brazil. Facebook has become the largest player on the global stage. The study found that Facebook's greatest growth has come from 35-49 year-olds, and it has added twice as many 50-64 year-olds as those under 18. Now that social media has broken out of the youth demographic, the search for a workable ad model is even more urgent, says the report.

"If the successful ad model can be found," says the report, "a significant shift in advertising revenue from 'traditional' online media towards social media could be realized."

The prevailing wisdom, concludes the report, is that the current level of advertising activity on social networks isn't consummate with the size and highly engaged levels of the audience. But, the Nielsen report says, advertising and social media to date have not been compatible. Advertising has typically performed poorly in chat and e-mail because of social media's communications role. The larger challenge for advertising is to move from an interruptive role to joining conversations, concludes Nielsen.

Member Communities' now reach over 5 percentage points more of the Internet population than it did a year ago, a growth rate more than twice that of any of the other four largest sectors.

Social networks online started out among the younger audience. As the networks have become more mainstream with the passage of time, the audience has become broader and older. Consequently, people under 18 years old are making up less of the social network and blogging audience, whereas the 50+ age group are accounting for more of the audience.

In terms of sheer audience numbers, the greatest growth for Facebook has come from people aged 35-49 years of age (+24.1 million). Facebook has added almost twice as many 50-64 year olds visitors (+13.6 million) than it has added under 18 year old visitors (+7.3 million).  If the average month-on-month audience changes over the last six months were to continue, by mid-June 2009 there would be as many 35-49 year olds on Facebook as 18-34 year olds.

The report concludes that a key reason why advertising on social networks hasn't been as successful as on the more ‘traditional' publishers is because social networkers serve as both the suppliers and consumers of content. In the traditional model they simply consume the content supplied by the publisher. Therefore, members have a greater sense of ‘ownership' around the personal content they provide and are less inclined to accept advertising around it. As the site becomes more attractive to advertisers it becomes less appealing to members who see highly-targeted ads as invading privacy.

For more about the study and to download the (free) full paper from Nielsen, please visit here.