The Chesapeake Digital Preservation Group has released "'Link Rot' and Legal Resources on the Web: A 2011 Analysis by the Chesapeake Digital Preservation Group."
Here's an excerpt:
The Chesapeake Digital Preservation Group has completed its fourth annual investigation of link rot among the original URLs for online law- and policy-related materials archived though the group's efforts.
The Chesapeake Group focuses primarily on the preservation of Web-published legal materials, which often disappear as Web site content is rearranged or deleted over time. In the four years since the program began, the Chesapeake Group has built a digital archive collection comprising more than 7,400 digital items and 3,200 titles, all of which were originally posted to the Web.