[Air-l] folksonomies

Hello, I am just beginning my PhD research and am interested in folksonomies/tagging/social bookmarking. Can anyone point me to research in this area? I have not been able to find too many references aside from general discussion on blogs. On the same token, I would also be interested in references that talk about the social construction of knowledge online. Thank you so much in advance for you help. Sincerely, Alla