One More Data Point
Safari Books Online is a service by technical publisher O’Reilly and Associates, that allows subscribers to their service to access their books, and those of several other publishers, online. (Highly recommended, BTW.)
Anyway, their front page lists the most popular books on their service. For as long as I can remember, the top book was David Flanagan’s Java in a Nutshell; but today, it has been displaced by JavaScript, the Definitive Guide (also by Flanagan, as it happens).
It’s notable mainly in support of Steve Yegge’s proposition that JavaScript is the Next Big Language. It is certainly popping up everywhere, and it is, for now, the only Apple-approved method of developing for the iPhone.
UPDATE: Okay, now both of Flanagan’s books have been displaced by a C# book. Please forget I said anything. :)