Choose a topic, let's browse History...
While browsing you are presented with title, author, year published, number of pages and a thumbnail of the book cover. Once you select a book you are presented with the reader interface and book content.
Considering that this is a web application (note, internet connection required to read, thus reading Google books on a flight will require prior planning, such as loading into Instapaper) the reader interface is sparse but acceptable, the navigation bar provides a contents button and page numbers (forward & backward navigation). The text is readable, touch once on the paragraph to see the original scan from the actual book. Photos and diagrams from the original text are also included and displayed via the web interface.
As noted earlier, you have access to over 1.5 million books, the texts are all public domain books, thus most of the texts are rather dated, you aren't going to find Grisham's latest here. But you will find many of the classics from authors such as Mark Twain, Benjamin Franklin, Charles Darwin, Rudyard Kipling, Jack London and Nikola Tesla. Once again, another great reference for your iPhone, be sure to bookmark it in Safari or add as an icon to your home screen.