It's less easy to find out about the impact of a book, although Scopus, Web of Science and Google Scholar all include citations for books. Google Scholar is probably the most effective way of tracking book citations. Simply search for the book in which you interested, and click on the 'cited by' link in the bottom left of the reference to find more recent articles and books which have cited it.
You can also demonstrate book impact through
Most Open Access activity so far has been focused on journal articles. However, various projects are emerging with regard to Open Access books, particularly in the humanities and social sciences. Various funding and licensing models are being explored.