As a student, I use Google Books all the time (particularly in conjunction with Google Scholar), so I am ecstatic about the new changes to the interface! For a quick overview and some nice screenshots, check out this post over at Google Operating System.
What I like about it is how clean it looks and how much easier it is to navigate a book! You can see the pages one at a time, like before, or side-by-side, as you would if you had the actual book with you, or see the whole books in thumbnails and jump around quickly, which I think would be particularly useful for books with pictures. I especially love the “Contents” drop-down menu, which essentially allows you to jump from one chapter to the next without constantly returning to the table of contents, which may or may not have links to the corresponding pages.
Also: the ability to switch between plain text and page images, or download the book as a PDF (granted, only available for certain books), is perfect since I’m constantly wishing I could copy-and-paste quotations into my notes!
Has anyone else played around with the new interface? Any cons the shininess has blinded me to?

