O'Reilly have stated that they are not interested in a book on OCaml at this time. They do not perceive that there is sufficient marketplace to support such a book.
There is a French O'Reilly book, but they have no intention of continuing to sell it or finishing and publishing the English translation.
O'Reilly's "so you want to write a book" guide for authors.
Richard W.M. Jones will write a proposal for an article for oreillynet.
Chromatic suggested the following topic for the article:
"Why OCaml rocks: show the high points, the stuff that OCaml makes easy, without getting bogged down in the language details. Point people to online documentation for the details."