For a few years, Google Book Search has provided PDF downloads of public domain books. The books came with a page listing some guidelines that Google asked people to follow and the same guidelines are listed in their Google Book Search help center. …

[The guidelines have been changed] – it used to say that only non-commercial use is [allowed]. Now it has been replaced by two new guidelines: no hosting, and no reprints including helping people reprint.

http://www.earlham.edu/~peters/fos/2009/02/google-dont-re-host-public-domain-books.html