2 scholarly articles discussing Wikipedia from the latest issue of the journal "First Monday":
http://firstmonday.org/issues/issue12_4/
The 2nd one has particularly interesting visualizations:
"Assessing the value of cooperation in Wikipedia" by Dennis M. Wilkinson and Bernardo A. Huberman http://www.firstmonday.org/issues/issue12_4/wilkinson/index.html
"Visualizing the Overlap between the 100 Most Visited Pages on Wikipedia for September 2006 to January 2007" by Anselm Spoerri http://www.firstmonday.org/issues/issue12_4/spoerri/index.html
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