After receiving an email mentioning a 987 page (!) genealogy of one of my families, I was feeling sad that it's out of print. Googling didn't find anything helpful, and WorldCat.org suggested helpfully that the nearest copy was in a library 187 miles away. But...clicking on the Editions link in WorldCat brought up a list of 4 editions of the book, one of which was said to be digital. And clicking on that brought up a link to the Hathi Trust website, where the entire book is digitized, searchable, and free for anyone.
Lesson: WorldCat.org is your friend.
And, if you're wondering, the book is The Basye Family in the United States, by Otto Basye, and the link is http://hdl.handle.net/2027/wu.89062852876
Oddly enough, while Google didn't find the digital version of the book, it did find a description of Otto's papers, which were donated to the State Historical Society of Missouri. Apparently there are approximately 4 shelf-feet of materials, largely the research for the book.