Reasonable book, but light on details - it refers too much to "go read the manpages". It's a good introduction to gitolite, but could explain in more detail some aspects. For example, when talking about triggers, it says: "“The important trigger points, from a customization point of view, are INPUT, POST_CREATE, and POST_COMPILE, although there are several other trigger points supported.” However, it doesn't list them. Then, at the end of the chapter, it mention as a single line a few other triggers - PRE_GIT and POST_GIT being very interesting, but not explained at all.
I know this is "essentials", and not "in depth", but I do think it should have gone into more detail. Still, I enjoyed it as a quick intro to gitolite, and time spent reading it was worth it.