Stanza's great feature is the ability to download copyright-free books to read on your phone. This feature uses the public domain to give access to thousands of books that otherwise would be out of print. It also gives you an easy way to buy books, but I haven't used that because I don't want my books encumbered with nasty DRM.
Lessig describes the problems with current copyright law, how by extending copyright terms indefinitely at the request of big corporations we are destroying the public domain, losing the 98% of works that make no money and are out of print so that the 2% left can be milked. All art borrows from the past, but we are moving towards a future where no art can be made without the permission of the big media companies who will own most of it.
He also provides some ideas on how to avoid this future. Limiting copyright terms, and requiring renewal for extensions, coupled with mandatory registration of copyright owners for a work would get rid of the problem we have now where nothing written since 1923 will fall into the public domain. Registration means that creators that wish to use a prior work would be able to work out who to ask permission of, something that currently requires lots of expensive lawyers. He also promotes the creative commons licences, which allow creators to specify which permissions they grant, rather than the blanket "all rights reserved".
The book was written five years ago, and things have changed a little. The big media companies are slowly dropping the DRM, and I haven't heard much about people being sued for downloading songs for a while. iTunes has shown that people are willing to pay for content on the Internet, and that you can sell it without DRM and the world will not collapse. The laws are still the same, copyright is still pretty much perpetual, but Lessig's work had made people think about change and that's a start.