I got "The Damian"'s PBP last year. Since the start of this month I've been working over some older modules. I've been doing my best to bring them up to "best practices".
Using a combination of the book, Perl::Critic, Module::Build, Devel::Coverage, I've found several no-ops in the code and some subtle bugs that had gone undetected.
I've added loads of tests and currently the first modules I've been really working on is now upto 98.7%, 87.5%, 73.7%, 100%, 100%, 100% and 93% on the test coverage stats. I've got no severity 5 PBP issues, only two severity 4s that I can't fix without changing the API, and I've reduced the number of severity 1, 2 and 3 issues by over half.
I know that following guidelines isn't a panacea for good code, but it's been an interesting process that does force you to think about your code. Is it really okay to deviate from PBP or the guidelines really better? I've also found some bugs, so it's been well worth it.