Perl is simply the easiest language to write heavy-duty code in. A line of Perl is a paragraph in any other language, and will probably run more efficiently as well. Perl has modules for just about everything. This is not to say that Perl is necessarily the best tool for every job - I prefer PHP for most high-volume, low complexity tasks - but Perl is definitely the best language for custom-designed code. I can throw together a rough draft of my application in an hour or two, juggle it around a bit, then rewrite in some other language once I've figured out what I want to do. If I tried to write in the other languages from scratch, it would probably take me days.