How is data from social networking sites being used for research?

In week 5 Nigel showed us some articles which demonstrate how social networks are being used by data research institutes. In the BBC News article "Researchers plunder social networks" professor Nicholas Christakis from Harvard University points out that "There's just a phenomenal amount of work being done that takes advantage of what I would call this passive, massive, data collection effort".

Since most of the social network users display their profiles publicly, researchers can examine the dynamic of online friendships, interest groups, etc.

"Facebook is particularly useful to sociologists because of the way members accurately record relationships. Friends can add applications to compare tastes in everything from films to music to books. That can help researchers establish whether people tend to form relationships with others who are similar to themselves."

http://news.bbc.co.uk/1/hi/technology/7187680.stm

Apart from sociologists, I would reckon that social networking sites such as Facebook and Myspace, etc. are also of major interest to brands, record labels, etc., since trends and interest groups can be monitored perfectly on these sites.