"A universal digital library is within reach … We owe it to future generations to try," was the message from Dr. Pamela Samuelson, former Pitt law faculty member in her Feb. 19  Sara Fine Institute lecture [at Pitt]. Samuelson...made the case that Google’s approach "got us closer than ever before to being able to achieve that."
For a concise synopsis of recent lawsuits concerning Google Books and HathiTrust read this University Times article by Marty Levine.
Q. How much of these collections are in the public domain?
HathiTrust: 3,334,521 volumes(~31% of total) in the public domain out of 10,677,593 total volumes. (April 2013)
Google Books: This information is not available from Google.
Internet Archive: Almost 3,000,000 public domain books and texts. (October 2012)
Q. What is my access to these collections?
HathiTrust: The ULS is an institutional partner and all of the public domain ebooks are downloadable as a PDF. All of the books are full-text searchable.
Google Books: All of the books are full-text searchable. Anyone can search and view the ebooks. Public domain books are downloadable via PDF.
Internet Archive: All of the books and texts are full-text searchable. Anyone can search and view the ebooks and texts. Public domain books are downloadable via PDF and eHub formats.
"HathiTrust is an international partnership of academic and research institutions dedicated to ensuring the preservation and accessibility of the vast record of human knowledge. The partnership owns and operates a digital repository containing millions of public domain and in copyright volumes, digitized from partnering institution libraries and other sources. The preserved volumes are made available in accordance with copyright law as a shared scholarly resource for students, faculty, and researchers at the partnering institutions, and as a public good to the world community." - from HathiTrust website
The University Library System (ULS) is continuing as a HathiTrust partner, and has configured the institutional authentication necessary to allow special services for affiliates of HathiTrust partners. Currently those are:
Directions to download the full PDF in HathiTrust.
Google Books searches and preview millions of books from libraries and publishers worldwide. Book Search works just like web search. Try a search on Google Books or on Google.com. When a book with content matches your search terms, it is in your search results.
If the book is out of copyright, or the publisher has given Google permission, you'll be able to see a preview of the book, and in some cases the entire text. If it's in the public domain, you're free to download a PDF copy.
You also have links to "Buy this book" and "Borrow this book" to see where you can buy it or borrow the print book from a library.
How Books Appear in Google Books:
Internet Archive is a non-profit digital library offering free universal access to books, movies, music, & computer software as well as 292 billion archived web pages. It has many different components and projects and was started in 1996.