I'd say that the biggest disadvantage to Perl is its history. There are just way, way too many "tutorials" out there based on outdated versions of perl and perpetuating bad, unsafe programming practices. Aside from misleading those who don't know enough Perl to know that there are better ways to write it, they also do horrible things to Perl's reputation (and, in some cases, that even spills over to harm the reputation of those who write in Perl).