Recs.
Updated
Specs
Pros
Pro Central, huge package repository
The CPAN is one of the largest and one of the first central repositories for modules written for a programming language. It hosts over 33 thousand packages, so to avoid reinventing the wheel you can always have a look for the problem you want to solve.
Pro Backwards compatible
Rumour has it that Perl is dead, but it's quite the opposite, there are regular updates with a major release every year. These updates however strive to not kill old code, while still add new things to the language. Perl 5 evolves without becoming a moving target, programming in it is not a constant learning process in the sense of dropping something from three days ago because today something else has to be used.
Pro Meaningful, easy to understand error messages
If you've seen pages long croaks from C++ before your compiler finally gave up and none of them was about what the actual mistake was, Perl also tries to make your error-hunting life easier with providing you a good description of what is what you shouldn't have done.
Pro Strict mode
While it seems like an afterthought (why would you need to manually enable it in any sensible language), strict mode and the warnings pragma go hand in hand and help you find your bugs and typos better. Care has been taken in Perl so that it can report many mistakes at compile time, that other dynamic languages can only do at run time.
Cons
Con Difficult To Reason About
Perl's semantics involve a lot of contextual variation, which leads to a lot of situational ambiguity. For one-off scripts and fairly straightforward, well-trodden coding ground, this can make it very easy to get things done, but it also lends itself to subtle bugs and, at times, thoroughly frustrating surprises in how a program executes.
Con Overly Complicated Implementation
Respected Perlist, author of well-regarded Perl books, and active core project contributor Nat Torkington has famously described Perl internals as "an interconnected mass of livers and pancreas and lungs and little sharp pointy things and the occasional exploding kidney." Need we say more?
Con Weakly Typed
While dynamic type systems can be used to great effect, weak type systems tend to cause problems by introducing ambiguity in the meaning of code, causing surprising effects due to unexpected typecasting, and generally making it a lot harder to understand the code and the current state of data within the software.
Con Restrictive License
The licensing status of Perl is abysmal. It seems probable that the biggest reason there has been no particular interest in making Perl embeddable in other applications as a scripting language is the fact its primary license is incompatible with almost everything.