Just a quick heads-up for those waiting on it: I have updated chapters 1 to 4 of the book for Yesod 0.7. Well, chapter 1 is just an introduction chapter, so that doesn't count. And chapter 2 is the Haskell overview, which just has a bunch of FIXMEs. So I didn't really do anything there.
But chapter 3 and 4 have real code, and they've been updated. In particular, chapter 4 has basically been completely rewritten: it completely covers Hamlet, Cassius and Julius. For those interested in the new syntax introduced in 0.7, please check it out.
As usual, comments are much appreciated so I know where to fix things.