I will be voting this up. I honestly believe that this post makes one of the most fundamental points about good programming technique that I have seen merlyn make. If you read books on programming you will hear it echoed again and again in many different ways.

The point is that the key to maintainability is to have each thing done in one place. You want to avoid using two parallel efforts. Not only is it duplicated effort, both originally and ongoing, but it is a significant maintainance problem.

The easiest route to code-sharing in the short-term is called cut-and-paste. However if you stay aware of where your energy is going and work to get to code-sharing through having any particular task done once in your code-base, you will find that decision paying you back time after time again.

For more on this I recommend virtually any classic, starting with The Pragmatic Programmer because it is not only classic, but also mentions Perl quite a few times. :-)