Social networks

One of the biggest particularity of the web 2.0 is the emregence of social networks. It can be seen as a space on the web where people exchange ideas, informations or opinions about general or specific topics. In those websites, there isn't any webmasters who are publishing content on the website anymore. Net surfers do it themselves. Wikipedia is a good example with 1,426,000 articles in english published by net surfers, Youtube, Dailymotion, Flickr too with different concepts. Maybe the oldest social network is the good old Forum (like this one) as we can see in most of websites where people discuss for years.