From The New York Times:
We’d better address one textual issue up front, and without italics. This book opts for the iconic form: OK. This newspaper’s style calls for the punctilious (and closest to the original) form: O.K. My own strong preference is the form that looks most simply like a word, whose pronunciation is clear, and which doesn’t call for an apostrophe in extensions like “okayed” and “okays”: Okay. (Capitalized only when it begins a sentence or a sentence fragment like this or the preceding one.)
OK/O.K./okay so far?
Oh, my. Maybe we should follow the precedent handed down in 1967 when the writers of a song entitled “Supercalafajalistickespeealadojus” filed a suit claiming that their copyright had been infringed by the song “Supercalifragilisticexpialidocious.” Wrote the judge: “All variants of this tongue twister will hereinafter be referred to collectively as ‘the word.’ ”Not that the word considered here is a tongue twister — anything but. Allan Metcalf, professor of English and executive secretary of the American Dialect Society, has made a strong case for his subtitle. He certainly establishes that “the word” . . . No, that’s not going to work. How about OK, a k a O.K. . . .