The Public Doman: Public Domain Trouble Spots
From the Standford University Libraries Copyright and Fair Use Site, this page is a good place to find out some of the subtleties of the public domain.
http://fairuse.stanford.edu/Copyright_and_Fair_Use_Overview/chapter8/8-b.html
Today there's a right column advertisement for Stephen Fishman's book The Public Domain, 3rd edition, and while I can find plenty of commercial web sites trying to sell the book, I'm still hunting up a review or some sort of critique worthy of putting here in the blog.