Mastering Perl is the next book in the Learning Perl and Intermediate Perl progession of books.
I wrote the book "transparently", meaning just about anyone was free to take part, review the intermediate drafts, or make comments. You got to see how a book goes from the idea to the final product, and I got a better book as a result. You can read the proposal, which started the project, join the Mastering Perl mailing list that has infrequent updates on Mastering Perl new, or peruse the mailing list archives.