It seems like PBP would be best as a continually updating online book. It is something that will keep changing as the years go by. Also, there are some techniques that the community don't want to encourage. (Inside Out Objects). Its a great book but most of it wouldn't be useful if you had just starting learning Perl. In a wiki format (or something similar) sections could be tagged as "Beginner", the community could have comment sections and such.