There's a new biography of Joseph Mitchell by Thomas Kunkel called "Man in Profile: Joseph Mitchell of The New Yorker." It's reviewed by Janet Malcolm in the April 23rd issue of the New York Review of Books. I had a copy of Mitchell's "Up in the Old Hotel" which I kept for years- such an eerie tale of old New York, before the Brooklyn Bridge was built.
I didn't know Mitchell, but I saw him fairly often. He liked to come to the 11 o'clock service at Grace Church, and lurk in the back by the narthex (that's foyer to the uninitiated). He didn't discriminate between Morning Prayer and Communion, never approached the altar rail. The Rev. Fleming Rutledge, the assistant at the time, told the congregation that Mitchell came for the sermon.
I never felt like Mitchell was approachable, so I left him alone. Never asked him about his writer's block, or about the New Yorker's glory days. He was a man who wanted to be left alone. And I was a young writer who didn't want to upset an old man.