Subclassing is a great tool for making small changes to a piece of code to fit it to new requirements. It is as easy as copying code - but it still keeps the new constructs synchronized with later changes to the original. There are problems with inheritance hierarchies - but you need to have a 'hierarchy', not just two classes, to get there.
I imagine that it would be perfect for extended configuration of applications - including web applications. Wouldn't it be great if you could run a slightly changed version of you main web app by making it's code available from PERL5LIB and then subclassing it to change the colors used, add some minor new features and remove some pages for and affiliated site? Or if you could install a blog engine from CPAN, and then subclass it to add new and override old features? This could even make distribution of CPANized applications more popular.
This is one of the things I am experimenting with at Nblog (see also the screencast: Experiments with inheritance in WebNano based applications).