ConsultantCommons.org has created a Social Bookmarking Tool Comparison resource in an effort to keep track of and compare social bookmarking tools. From their site:

"Introduction Purpose
This article looks at the evolving crop of social bookmarking tools, their functionality and examples of use. The goal is to help nonprofits understand the value of using social bookmarking tools and to determine which social bookmarking tool would be serve their needs. This is directed at nonprofit uses of these tools."

Read more at http://www.consultantcommons.org/node/239

[via Depraved Librarian]