Aside from general excitement over having a good dead-tree ANTLR reference available, there is a cool thing I noticed in the PDF. All the code samples are linked to, what I presume will become, the text form online!
Note the "Download tour/eval/Expr.g" at the top. That is a live link in the PDF. It 404's right now, but I presume when the book is released the code will be there. That rocks. The normal "download the ode at http://example.com/foobaz.tgz" and dig through the tarball ~works, but a live link directly to the correct context is way better.