Mark Twain's autobiography, which he instructed should remain unpublished until 100 years after his death, is coming out this fall! It should be worth the wait.
Why the long delay? Apparently, Twain spoke/wrote rather freely about certain people. Also, he knew some of his views would be unpopular:
"He had doubts about God, and in the autobiography, he questions the imperial mission of the US in Cuba, Puerto Rico and the Philippines. He's also critical of [Theodore] Roosevelt, and takes the view that patriotism was the last refuge of the scoundrel. Twain also disliked sending Christian missionaries to Africa. He said they had enough business to be getting on with at home: with lynching going on in the South, he thought they should try to convert the heathens down there."
If he thought that the US of a hundred years later would agree with him, he badly miscalculated. If he thought we would need to hear this just as much now as in his day, he was remarkably prescient.
(Via Record and Archives in the News)