The 2nd beta (B1...) of Christophe's upcoming book, "Prototype and script.aculo.us," was released yesterday by the Pragmatic Programmers. It now features the whole contents about script.aculo.us, and is 95% content-complete.
At about 390 pages, it's close to its final size, the only missing elements in there currently being 4 tiny Trac commits and the to-be-coded stuff for Prototype 1.6 (such as custom events).
All existing readers got an e-mail notifying them of the update and providing a link so they can generate their updated PDF. If you haven't grabbed it yet, now is the time!