|laziness, impatience, and hubris|
To me Perl, Python and Ruby are pretty much the same thing.
Some people prefer Perl, others Python, it is (mostly) a matter of taste.
Perl seems to be a little faster (when your script is counting up to a billion it could save you a few secs) but as most apps are network-bound anyway this is irrelevant.
Perl has a slight edge with regard to libraries as (I believe) what Python and Ruby have do offer does (not yet) match CPAN.
For Python and Ruby however there are interpreters written in Java and I think that holds some promise - and a Java-interpreter for Perl will not happen any time soon (if ever).
For me the most important reason for using Perl rather then Python or Ruby is "market-penetration".
For instance nowadays (I think) you cannot build a Linux-kernel without Perl, and Perl comes with some comercial software as well (e.g. ClearCase brings it's own Perl).
So bottom line for me: It's hard to ignore Perl (at least if you work on Unix), so why not use it everyday?