Google has added a few interface niceties to its Book Search book viewer. It now loads multiple pages at a time, giving readers the option of either scrolling down or paging through left to right. There’s also a full screen reading mode and a “more about this book” link taking you to a profile page with links to related titles plus references and citations from other books or from articles in Google Scholar. Also on the profile page is a searchable keyword cluster of high-incidence names or terms from the text.

Above is the in-copyright Signet Classic edition of Billy Budd and Other Tales by Melville, which contains only a limited preview of the text. You can also view the entire original 1856 edition of Piazza Tales as scanned from the Stanford Library. Public domain editions like this one can now be viewed with facing pages.
Still a conspicuous lack of any annotation or social reading tools.