6/10 top internet sites are social (youtube, live.com, facebook, hi5, wikipedia, orkut); none were on the list in 2005
The number of Britons joining a social network is expected to treble from 9.6m to 27m by 2012, according to Datamonitor.
The market analyst predicts the UK to see the strongest growth in Europe over the next five years.
France, which at 8.9m has the second highest number of social networks, is estimated to reach 21.3m by 2012.
Europe is expected to see a jump of 41.7m to 107.4m by 2012.