And from Geeking with Greg:

http://glinden.blogspot.com/2005/06/yahoo-gets-social-with-myweb.html

http://glinden.blogspot.com/2005/10/getting-crap-out-of-user-generated.html

http://glinden.blogspot.com/2006/01/digg-spam-and-most-popular-lists.html

http://glinden.blogspot.com/2007/02/combating-tag-spam-paper.html