The naming conventions used for files in the book are the ones I like to use in my live projects. So, if you don't like spaces or capitalization, use whatever makes sense to you. As for whether it's good practice, well, that's subjective to your own personal opinion.
I've heard that some people have gravitated toward using dollar signs to name global variables, and not using a dollar sign for variables created in local scope (i.e., within a function or class method). I think that probably makes more sense. But, like I said in the book, my own habits came from PHP.
I'm sorry for the late reply, BTW, I noticed your post, but forgot to reply.