The phrase "on book leave" has been popping up here and there (especially in the New York Times) recently. I presume it refers to a sabbatical taken for the purpose of writing a book, rather than for the purpose of promoting (or reading, for that matter) a book. Correct?
It gets only 75 hits on Google, of which more than half refer to NY Times columnist Maureen Dowd.
The phrase "on book leave" has been popping up here and there (especially in the New York Times) recently. I ... purpose of writing a book, rather than for the purpose of promoting (or reading, for that matter) a book. Correct?

Yes. It's used in professions where one might be expected to write a book, such as journalists and academics. Engineers are expected to write their books while working.
OTOH, "gardening leave" is a mealy mouthed euphemism for "suspended on full pay".

David
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