In a language like Perl, one that insists on being richly pluralistic, you need some guide that points you towards what practices are conventional, clear and maintainable. PBP provides that, and is well written and insightful as well.
We have one copy at work, and we would have more if we didn't have it available on-line on Safari. I also bought my own personal copy for home.
The book has allowed me to write code with confidence that it will be generally understood, and it will be easier for people to find things in it in an emergency. It has also guided me towards which modules are mainstream, or may become so.
It has changed how I write C, and other languages, but it has also reduced my tolerance for writing in other languages.