Google Book Search has been surprisingly useful in identifying ancestors who might have contributed to a book or who might be mentioned in the text of a book. ... "Genealogical research can be complicated by the fact that some books are so rare, the likelihood that you'll find them in even a single library is fairly low. ... If you, your patrons or students are interested in researching your family history, I encourage you to give Google Book Search a try at http://books.google.com. Especially if you've got a fairly unusual name (sorry to the John Smiths out there), enter your name and see what happens."
Complete text of article may be accessed here: http://www.google.com/librariancenter/articles/0606_02.html
