I think Perl's real strength is that it makes "easy things easy and hard things possible" for not a single domain, but for many. Perl is a generalist language; many people call it a glue language becuase it can interface in to many different protocols, systems, and data stores. But calling Perl 'glue' is a bit disparaging. Glue is usually used to hold interesting bits together, but is not interesting itself. Typically interfacing disparate systems and doing something useful with them is more substantial. I prefer 'infrastructure'.

Some people say Perl excels as a text processing language; with its wide range of string, regex and formatting functions, I agree. But I use Perl mostly for scientific and number crunching. Writing such code is fast and easy with modules like the Perl Data Language. Although I used to program in domain-specific Fortran, Perl is far more pleasant and flexible.