Social Networks and blogs are visited by over two-thirds (67%) of the global online population, making them the fourth most popular online category ahead of email, this according to Nielsen‘s new “Global Faces and Networked Places” report.

The social network and blogging audience is also becoming more diverse in terms of age: the biggest increase in visitors during 2008 to “Member Community” web sites globally came from the 35-49 year old age group (+11.3 million).

Meanwhile, mobile continues to play an increasingly important role with 23% of users in the UK reporting using mobile devices to check their networks, compared to 19% in the US (10.6 million people). Facebook, now the world’s most popular social network,  is visited monthly by three in every 10 people online across the nine markets that Nielson tracks.