I’ve made a couple starts on books but so far haven’t been able to stick with it long enough to finish; it becomes too tempting to release content as examples or smaller articles. And while those are useful, too, piecemeal content lacks the cohesiveness / comprehensiveness / depth of a book… so I’ll keep trying and hopefully find a way to make a book in the future.
(And by “book”, I’m including online publications like Mark Pilgrim’s excellent /Dive into HTML5/. I’d almost certainly publish online given the interactive nature of the subject.)