Reason I'm asking this is my observation (which may be subjective) that developers tend not to take a language for real until someone has written a book about it. Books about Ruby, Groovy and other languages appeared way after those languages gained popularity, but the masses don't decide to go for it if there is even no single book about it. I just saw that the Ceylon guys are planing a collection of articles, docs from their homepage as a book (see link). I think the book about Scala was out at some Devoxx. People were rushing after it at the conference and it was sold out in record time. Think that gave some momentum to Scala back then.
Cheers, Oliver