If the pre-1976 law were still in place then as of Jan 1, 2012 the following books, movies and music would have entered the public domain (from the Center for the Study of the Public Domain):
J.R.R. Tolkien’s The Return of the King, the final installment in his Lord of Rings trilogy
C.S. Lewis’ The Magician’s Nephew, the sixth volume his The Chronicles of Narnia
Vladimir Nabokov’s Lolita
Jerome Lawrence & Robert E. Lee’s play about the Scopes “Monkey Trial,” Inherit the Wind
Isaac Asimov’s The End of Eternity.
Jack Finney’s The Body Snatchers
The Seven Year Itch, directed by Billy Wilder; starring Marilyn Monroe and Tom Ewell
Lady and the Tramp, Walt Disney Productions’ classic animation
Alfred Hitchcock’s To Catch a Thief, starring Cary Grant and Grace Kelly
Richard III, Laurence Olivier’s film version of the Shakespeare play, co-starring Claire Bloom, Cedric Hardwicke, Nicholas Hannen, Ralph Richardson, and John Gielgud
Under the old law, the above works could not only have been consumed they could also at low cost and without requiring the express permission of the original copyright holder have been remixed, reworked and extended in new directions. Under the new regime, innovators will not be able to easily build on these works until 2051 and it could be well into the 22nd century before we get Star Wars prequels worthy of the name.