If Volume 4 has been a long time coming, Knuth has not been idle. Unlike most books, Volume 4 will not appear all at once. Instead, 128-page fascicles will be released more or less as Knuth finishes writing them. Though not scheduled for publication until 2000 or later, the fascicles are sure to begin circulating informally before then. It could be a decade or two into the next millennium before he completes the set.
Nobody has to say more than that, who the author is, what book they're talking about.
Speaking with Knuth, one gets the impression of a man hard pressed to keep up with his mind's high-speed output of ideas. Besides demonstrating the techniques of clear, efficient coding, Knuth has sought to bring a deeper sense of aesthetics to the discipline. I'm hoping someday that the Pulitzer Prize committee will agree. Knuth himself has already collected numerous awards, including the National Medal of Science from then-President Jimmy Carter and Japan's prestigious Kyoto Prize. At Stanford, Knuth no longer teaches, though he occasionally lectures on whatever happens to interest him at the moment.