This is the sort of book I like, easy to read, lots of code examples, and even more description on how things work. It starts easy enough, installation of mod_perl and the generation of code. Each section handles a single subject starting from the bottom and working up, again from the most widely used to the more esoteric. There's a nice list of 'almost' all of the constants and a list of resources at the back. The book is backed up with examples on their web site.
The layout is clean and easy to read with short code examples that are fully runable.