Most tasks only require a small subset of the Perl language. One of the guiding mottos for Perl development is ``there's more than one way to do it'' (TMTOWTDI, sometimes said ``tim toady''). Perl's learning curve is therefore shallow (easy to learn) and long (there's a whole lot you can do if you really want).
Finally, Perl is (frequently) an interpreted language. This means that you can write your programs and test them without an intermediate compilation step, allowing you to experiment and test/debug quickly and easily. This ease of experimentation flattens the learning curve even more.
Things that make Perl easier to learn: Unix experience, almost any kind of programming experience, an understanding of regular expressions, and the ability to understand other people's code. If there's something you need to do, then it's probably already been done, and a working example is usually available for free. Don't forget the new perl modules, either. They're discussed in Part 3 of this FAQ, along with the CPAN, which is discussed in Part 2.