Here's one big thing: I have been trying to read it on a Kindle Paperwhite (A stretch, I know, for a programming book, but I worked hard to make Atomic Scala work on it because I know for a lot of people, including me, it's the nicest reading tool) and it's gotten to where I can't anymore, because of the way they handle comments -- which are greyed out to the point where they are basically unreadable. I don't know what control you have over this but you should at least give O'Reilly feedback so they know there's a problem. They should be testing on that, and this makes me think they aren't. (via private e-mail to LR)