Necessity being the mother of invention, I really started learning Perl when I had to write Perl. Most of the Perl I was maintaining wasn't very well written. As examples it could only take you so far.

The most effective tool for learning in recent times has been reading PerlMonks and trying to answer questions within my ability, and then reading the answers of others. There is nothing quite as effective as an ever changing pool of questions to sharpen your skills on, and an ever changing collection of questions and answers to ponder.