Use WorldCat to compile a list of libraries that own the book in question. WorldCat gives the truest indication of the total number of owning libraries. Search by author, title, or ISBN (unique book number). Look for "Libraries Worldwide" in the bibliographic record. The list of owning libraries can be emailed or printed for later analysis.
Google Scholar incorporates a cited reference search that is upending our traditional reliance upon Web of Science. No comprehensive analysis of an author's corpus can afford to overlook Google Scholar. Look for "Cited by X" in the relevant citation of the Google Scholar results list. Note that Google Scholar is the best tool for analyzing the impact of a book or a book chapter as opposed to a journal article. Traditionally it has been very difficult if not impossible to analyze the impact of a book, so this is yet another way in which Google Scholar is changing the game.
Google introduced a "limited launch" of Google Scholar Citations on July 20, 2011. The company opened up the database to anyone interested in creating a profile on November 16. Like the more traditional Web of Science and SCOPUS databases, Google Scholar Citations tracks citations to scholarly publications. But unlike WOS, Google Scholar Citations tracks a range of scholarly works from conference proceedings to books. It is easy to create a profile and well worth doing so, in my view, with one caveat: Google has a spotty record of supporting projects with a necessarily limited audience (recall, for example, the unfortunate consequences of Google's acquisition of Paper of Record).
MLA International Bibliography (MLA), JSTOR, and ProjectMuse can all be extremely useful for finding scholarly book reviews, as can the interdisciplinary database Academic Search Complete. These databases cover, in addition to book reviews, scholarly journal articles, dissertations, editorials, and speeches, so you will likely wish to limit your results to book reviews. Unfortunately, no designated book review field exists in MLA, but the phrase "review article" is often used in a record's subject field for this purpose. It is easy to limit your search to "Reviews" in JSTOR.
The following is a dedicated book review databases: