I have written about the Kirtas Technologies book scanner, which can scan up to 2400 pages per hour. Yes, that device scans one page every one and a third seconds. Place a book into the device, press a button or two, and then walk away. You can return a few minutes later to find the entire book has been scanned and the data stored on the attached Windows PC. You don't even need to cut the bindings of the book as the device turns the pages and makes images as needed. You can see my pictures of this $120,000 book scanner in operation at http://blog.eogn.com/photos/ala2007/kirtasbookscanner1.html and at http://blog.eogn.com/photos/ala2007/kirtasbookscanner2.html.
Kirtas (pronounced KEER-tass) Technologies apparently isn't content to just make the scanners; the company also makes many out-of-print and out-of-copyright books available to customers, including a number of genealogy books. You can download a book to your computer's hard drive and read it there or even print pages from the book on your local printer. Another option is to have the entire book printed "on demand" and have it shipped to you.
Prices vary depending on the length of the book, but this is often the only method of obtaining a desired book without travel to a library that might be thousands of miles away.
I did a search for the word "genealogy" on the Kirtas Books web site and found many such books available, including A biographical history of the Eby family, being a history of their movements in Europe during the reformation, and of their early settlement in America; as also much other unpublished historical information belonging to the family (printed in 1899, 144 pages for $1.95), and A complete record of the John Olin family, the first of that name who came to America in the year A.D. 1678 (printed in 1893, 228 pages, for $1.95). These are but two examples of the many genealogy and family history books available.
Kirtas has an interesting option called "Invest in Knowledge" that can offset the price of digitizing a book for the first time. The program allows anyone to subsidize the digitization of one book and then to receive 5% commission on all future sales of that book through Kirtasbooks.com. You will receive a reprint of that book as well as the ongoing 5% commission.
Assuming that a book has not yet been digitized, you will need to find the book in one of the participating libraries. You can start your search on Kirtas Books' web site, which links to WorldCat, an online catalog of books held at libraries around the world. You then select the book that you want. Kirtas Books' employees or contractors will pull the book from the shelf, scan it, and then deliver it to you as a soft-cover, printed "book on demand." You pay the full price for that one book.
Kirtas Books then retains the electronic image of the book you selected. Kirtas will add it to the company's inventory, and you can (optionally) also promote the same book on your web site or by any other means available to you. Every time someone orders "your book" from Kirtas Books in the future, you receive a 5% commission. You can learn more about Kirtas Books' "Invest in Knowledge" program at http://www.kirtasbooks.com/index.php?option=com_content&view=article&id=12&Itemid=11.
All in all, I'd suggest this is a good method of obtaining long out-of-print books. I would probably always start at Google Books, simply because it has hundreds of thousands of books available free of charge. However, if I was unable to find what I wanted on Google Books, I would move on to Kirtas Books and to other online catalogs of old books.
You can learn more about Kirtas Books at http://www.kirtasbooks.com. Frankly, I found the web site to be confusing but the information is there, if you want to hunt for it.