In most countries, policies for evaluating research outcomes tend to privilege peer-reviewed journal articles over scholarly books. There are signs, however, that there might be some shift in the balance. In UK there are some signs that the Research Excellence Framework (REF) may be somewhat more catholic than the 2008 Research Assessment Exercise (RAE).
Research evaluation tends to give some role to bibliometrics (not least because counting citations is often less expensive than alternative methods such as peer review). There is a difficulty here, however: bibliometric data sources are much better developed for journal publications than for monographs.
For this reason, news of moves towards the development of indices for scholarly books is welcome. In particular, the announcement from Thomson Reuters that they will be launching a book citation index later this year (2011) is welcome. Not all details concerning this development are yet known, but the Thomson Reuters website includes a facility for registering for updates.