O'Reilly Media, announced the migration of its book about Wikipedia to the English language Wikipedia. As of today, the entire contents of Wikipedia: The Missing Manual (O'Reilly, $29.99) by John Broughton is available for free online for editing and updating just like any Wikipedia entry.
I think this is a great news. I have read the book and it is excellent. This way it becomes even better and more useful. The Missing Manual can be found on en.wp.Help:Wikipedia: The Missing Manual.