Google is a great resource for genealogists on many different levels. Google Books, provides digitized books including new genealogy how to books, older history and genealogical books, and all kinds of non-fiction books. To search Google Books, just go to http://books.google.com/ and search for a locality, a name, or a subject.
Newer books, will not be completely digitized. These are protected by copyright so you will find only a percentage of the book digitized and available. Older books, prior to about 1923 may be completely digitized.
I have had at least one person tell me of finding her ancestor in a family history book on Google Books with information she had not found previously. This is a great resource for genealogy whether you researching a family or want to learn more about research techniques.