This, covered at the Official Google Book Search Blog.
While it is easy to share links, photos, videos, and opinions on the Web, sharing books with your friends online used to be tough -- and tougher even, to share individual clippings from a book. This summer, I worked with the Book Search team to add clip-sharing features to Google Book Search.
You can now highlight a section of text in any public domain book in Book Search, create a clip from it, and share it with the world. You can post your favorite clips to your blog along with a personal annotation, collect them in a Google Notebook, or share them with friends anywhere you decide to embed the link. Your clip looks exactly as it appears in the book, or if you prefer plain text, we have that too.
Also at the Official Google Blog, about collecting, sharing and discovering new books.
We've also launched a way to let users, select, copy and embed segments of public domain books (like the Newton quote) in any web page. We hope to make it as easy to blog and quote from a book as it is from any web page. Like many innovations at Google, a stellar summer intern worked on this.