Martin Schneider writes:

Here's the lede from "The Death of the Slush Pile," by Katherine Rosman, in the Wall Street Journal:

In 1991, a book editor at Random House pulled from the heaps of unsolicited manuscripts a novel about a murder that roils a Baltimore suburb. Written by a first-time author and mother-to-be named Mary Cahill, "Carpool" was published to fanfare. Ms. Cahill was interviewed on the "Today" show. "Carpool" was a best seller.
That was the last time Random House, the largest publisher in the U.S., remembers publishing anything found in a slush pile. Today, Random House and most of its major counterparts refuse to accept unsolicited material.

(After I wrote the above, it occurred to me that I should find out how Random House got its name. According to Wikipedia, "Random House was founded in 1927 by Americans Bennett Cerf, Christopher Coombes and Donald Klopfer, two years after they acquired the Modern Library imprint. Cerf is quoted as saying, 'We just said we were going to publish a few books on the side at random,' which suggested the name Random House.")