The Digital Curation Centre has released Web Archiving.
Here's an excerpt from the announcement:
The DCC has produced a report that provides a snapshot of the state of the art of Web archiving in early 2010, noting areas of contemporaneous research and development. It should be of interest to individuals and organisations concerned about the longevity of the Web resources to which they contribute or refer, and who wish to consider the issues and options in a broad context. The report begins by reviewing in more detail the motivations that lie behind Web archiving, both from an organisational and a research perspective. The most common challenges faced by Web archivists are discussed in section 3. The following two sections examine Web archiving at extremes of scale, with section 4 dealing with full-domain harvesting and the building of large-scale collections, and section 5 dealing with the ad hoc archiving of individual resources and small-scale collections. The challenges associated with particular types of difficult content are summarised in section 6, while methods for integrating archived material with the live Web are reviewed in section 7. Finally, some conclusions are drawn in section 8.