I have bought the pre-print verson of the PDF + paper book yesterday (26 Feb 2011). I've been reading the PDF and found a number of small errors:
section 2.2 page 29: "Of course" must be "Ofcourse".
section 4.2 page 44: Figure 4.2 is not in sync with Listing 4.1 and the text; "PostFrom" must be "UserPost" (and the Post message is not in the figure).
section 4.2 page 46: Listing 4.4 you need to import scala.actors.Actor._ to make this work ("actor" and "receive" must be in scope).
section 4.3 page 46: "... supports both asynchronous and synchronous messages sending": it must be "message", not "messages".
section 4.3 page 46: Sub-heading "Asynchronous messages sending": it must be "message", not "messages"; or the word "sending" should be removed. (Note that on page 47 it only says "Synchronous messages" without "sending").
section 4.3 page 46: Code sample at the bottom of the page: Isn't it necessary to call start() on chatRoom before you send it a message?
section 4.3 page 47: It looks like Listing 4.6 is to be placed after the sentence "Listing 4.6 illustrates how ... a Post message:" (which ends with a colon) and the following sentence "Note that there are two actors in the above example" (the listing is not actually above that sentence).
section 4.3 page 47: "... and makes it possible for subscriberActor", there is no subscriberActor in the listings, should probably be "sessionUser".
section 4.3 page 50: The text says that the timeout is 3 minutes, but in Listing 4.8 it is 1800 seconds which is 30 minutes.
section 5.2 page 56: (bottom of the page) "a call to react never return normally": it should be "returns".
section 5.3 page 61: "We obtain a future using the ! message send variant." That should be "!!", not "!".
Chapters 8, 9 and 10 are not filled in yet at all.
Hope this is useful for the authors to make book better when it really comes out.
The website still mentions 1 February as the expected print date, which is already almost a month ago. When is the book expected to come out?