in reply to What's the most important thing to learn in the Perl world?

Just my 2 cents:

If you haven't learned strict yet this is a must. It can be very tricky for people who is used to code loosely (believe me, I know =;c).

If you already mastered strict, then IMHO Regular Expressions are definitely the way to go. It's one of Perl's most charming features and they can do wonders.