Google have updated their Book Search “In an effort to make online book reading easier”. I think it worked.
Check out Nathan Naze’s Google blog entry: A new way to browse books, where he explains that you can now:
• Zoom in (and out)
• View the whole book on one web page (so you don’t have to load a new page for each new page)
• View the book two pages at a time (like an actual book)
• Scroll through the book using the scrollbar or your mouse wheel, or keyboard
• Find other books of interest
• See other books which cite or refer to a book.

It all sounds good, and from what I’ve tried so far, looks pretty good too.

• The zooming-in function is great, because it works quickly and easily.
• Having the whole book on one page, so you don’t have to click to the next page, is great, and makes it much easier to read, though the book I tried (Mansfield Park) was still a bit slow (a few seconds, but enough to interrupt the flow) to load up, even if it was all on one page.
  (Plus, there are still problems with the actual scans of the books: )
• The two-page view is ok – makes you feel almost like you’re reading a real book – but you can’t scroll down to the next two pages, you have to click on the arrow button to move on, which is a shame.
• Navigation (in one-page view) is easy. You can scroll through in lots of different ways, scrollbar, mouse wheel, pressing the space bar or page down moves you to the next page – or rather to the line above the last visible line, so you can find your place easily. But, you can’t go through by Chapter though, just by Section, which seems arbitrary (eg in Mansfield Park Section 2 is Chapter VI).
• They have cleaned the page up a bit too (except for the navigation and buy this book stuff) – and what is even better you can view in full screen and get rid of everything but the book and the page navigation. Or, you can download as pdf.
• The information (About this Book) page has changed too – this is where you can see related books, books and scholarly works which refer to the book. Plus you can search within the book, and click through to view the full (or preview) text.

For more articles see:
Inside Google Book Search – What we’ve been working on

Greg Notess, SearchEngineShowdown – New Google Book Viewer

Search Engine Watch Blog: Google Book Search Catches Victorian Plagiarists

And to keep up to date with changes, check out the Google Book Search Blog.

To compare with the old version, take a look at these screenshots.