That depends on country, though - England and the US are life+70, Canada, Australia and Taiwan are life+50. That's why you can find things like EJO books and Dorothy Sayers on the Faded Page site (which is associated with Project Gutenberg Canada), and the Emily of New Moon books on Project Gutenberg Australia, but not on the main Project Gutenberg site (which is US based).
Faded Page is actually associated with Distributed Proofreaders Canada (DPC), not Project Gutenberg Canada. DPC do still publish some of their works at Project Gutenberg Canada, but mainly post their finished work at Faded Page.
Copyright law is a bit complex - in general, books published 1922 or earlier are in the public domain in the USA (no matter when the author died). Otherwise it depends if they renewed the copyright. In Australia, authors who died before 1950 are in the public domain, otherwise it is life +70 (life +50 until 2004, but the change isn't retroactive). The different Project Gutenberg sites only have books that are in the public domain in the country in which the site is hosted.
Disclaimer: I volunteer with Distributed Proofreaders (http://www.pgdp.net
) which post etexts to the main Project Gutenberg site, and I'm also a member of Distributed Proofreaders Canada (http://www.pgdpcanada.net