To effectively work on a large project you've got to manage complexity, with perl unless you are very strict, the complexity gets away from you. The thing is most programs start 'small' (I'll just write something that parses subscribe/unsubscribe requests and updates a sendmail alias) but ends up growing over time into a monster (majordomo...) Compared to almost any other language, Perl makes you spend a lot of time working with the irrelevant. 

  

 ''Perl let's you know about the reference as well as the reference. Other languages hide the reference from you without working fundamentally differently. How is that better?'' --AristotlePagaltzis 

  

 !!There's More Than One Way To Do It 

 Perl people say this is a good thing, but the problem with theres more than one way to do it, is that noone ever does it the same way twice. To properly read a program you have to understand the 'idioms' that that program is written around. In Perl it's difficult to realise that "ah, thats a switch statement, I can see what that's going to do" because in perl there is no switch statement, you can roll your own (a nice idea), but, you can get half way through and discover someone's modified their idea of a switch statement slightly and now it has a side effect you didn't realise until you read the code very very carefully. In most languages you can learn a couple of constructs (for, while, do..until, if...then...else, functions) and you've learnt a good chunk of the language and can read most of it. (Even C++ which has a huge number of things (virtual private classes? who on earth would use such a thing?) you learn about the various flow control structures, and how to define/call functions/methods, and you can follow a good chunk of C++), however in perl, since theres so many ways of doing anything you have to learn all the idioms before you can read a sizable chunk of perl code since they are all used, randomly.