Google Books 'my library' button doesn't just allow you to catalog the books you own on their site, but also allows you to search those books electronically.
From the TYWKIWBDI blog:
"Most web users are at least marginally aware of Google Books. I frankly had not been aware that the site has a "my library" feature, which allows you to import the books you have on your own bookshelves. You can do this by searching Google Books for the title you have and then clicking "add to my library," or you can go to your library list, click import books, and type in the ISBN. The video above also shows that with a handheld scanner (or using your computers webcam and appropriate software) to can rapidly add large numbers of books to the database.
The advantage of compiling "your library" in this fashion is, of course, that when you search Google Books for a keyword or phrase or topic, you can opt to search only the books you already have at home. Nice.
Info found at The Centered Librarian, a blog created by/for librarians but of interest to any serious bibliophile."
You don't need a handheld barcode scanner to enter books into 'my library'. search for the book by title and then click the 'my library' button to add the book. Like the blog's writer, I had no idea what "my library" did for me. Now, I can use Google books to search my print books electronically. It's the best of both worlds!
note: I know I've posted this information on numerous boards and discussion groups--but I think this information bears repeating.