I am responding to Bill's invitation (Portals and KM) by offering the following resources.
Here are my favorite resources on social tagging in a corporate context and more on tagging. I have also written on topic a while ago. This article from InfoTangle on Community 2.0 is also well written and I like the many clarifications it offers. The latest I have read about dogear is here (see my comment waayyyy below - it's a long and funny article).
Because social tagging is intricately related to folksonomies, folksonomies resources are also useful to take a look at.
PS: Bill - I had to answer here because your comments do not accept the "a" tag. ;-)