I started with Perl back like 18 years ago when I was still a teen. Needed to learn it so I could modify Matt Wright's WWWBoard, which was all the rage back then but looked like crap. I bought How to Learn CGI Programming with Perl 5 in a Week, which actually did teach me enough in a week to muddle my way through WWWBoard, but my level of skill was still laughable at best. Some years later I ran across Perlmonks, spent six months to a year studying code solutions and posting my own every day, and gradually got pretty good at the syntax and algorithms, even if modules were still a bit of a mystery. Fast-forward to five or six years ago, and I got a client who needed messy data from a variety of ancient systems cleaned up and imported to a relational database format, then searched using highly complex queries, so I figured the data munging aspects made this a job for Perl. A year and much pain and suffering later, we had the basic system put together. I learned how to make my own modules (more or less) and install other modules. Been upgrading the system periodically ever since.
in reply to How many man-hours would you estimate you have invested in learning Perl?
Given, I prefer PHP for more presentational sites, but any job that requires a lot of regular expressions, nested sorts, etc. is a job for Perl. PHP's syntax, especially in the area of sorts, is just so much more clunky. And since I can run Perl natively from Terminal on my Mac, it's more convenient for small one-off data-conversion scripts.
Short version - probably thousands of hours total.