‘Member Communities’ have overtaken email to become the fourth most popular online category, according to a Nielsen Online report.

Comprising both social networks and blogs, ‘member communities’ are now visited by over two thirds (67%) of the global online population and are growing twice as fast as any of the other four largest online sectors (search, portals, PC software and email), according to the ‘Global Faces and Networked Places’ study.

The findings also indicate that time spent social networking is growing at three times the overall internet rate, accounting for almost 10% of all internet time, and that 35 to 49-year-olds are the fastest adopters of member communities.

Australians’ access of member communities lags a little behind global trends – although social networking and blogging activity was up 4.9% in 2008 to 59.9%, it remained around seven percentage points behind the global average, ranking Australia eighth out of the 10 countries surveyed.

“Social networking is becoming a fundamental part of the global online experience. While already two thirds of the global online population accesses member community sites, the vigorous adoption and migration of time shows no signs of slowing, and in Australia we certainly expect strong growth moving forward to bring us in line with global averages,” says Melanie Ingrey, director of market research for Nielsen Online.

According to the Nielsen report, Facebook is visited by three in every 10 internet users every month across the nine markets in which Nielsen tracks social networking use. Orkut in Brazil has the largest domestic online reach (70%) of any social network in these markets.

In Australia, social networkers spent an average of nearly three hours per month on Facebook, which is up from one hour per month versus the previous year.

The Nielsen report noted, however, that while Facebook has experienced extraordinary subscriber growth, it hasn’t necessarily been accompanied by a similar surge in advertising revenue.

In comparison, MySpace’s slower growth but more entertainment and content oriented offering has attracted more advertisers.

“We felt compelled to analyse the state of the social networking market globally and consider what implications this has for our publisher and advertiser clients,” explains Ingrey.