I think it boils down to

• How people learn best, and
• What situation they're learning Perl in.

My first job coding in perl was a matter of picking apart code and understanding it; I had to do that before I could even think about refactoring, rewriting as modules, etc. I was pretty much just thrown into it, and expected to pick it up and troubleshoot things quickly. In this case, I found Perl in a Nutshell a godsend, as I could get quick answers to questions like, "What does the =~ do?" or "How do I assign values to a hash?". Oh, and the Perl Cookbook was nice, too, for that. Since I also learn better by examples, I found these very useful.

As my interest in Perl grew and I had more time to think and learn about *why* things were the way they were, and I also realized the code I was working with was pretty monolithic, with little or no use of modules, I found the Camel to be more useful. PBP wasn't around for me then, but I think it'd be somewhere in between - it's a good balance of examples and explaining of *why*.