Even though its only indirectly related I thought it was worth making a minor point:

Dont get too caught up in the OO aspect of Design Patterns. Perls functional abilities bring an entirely different view to how things like this can work. For instance the observer pattern works just fine with closures as callbacks, and has the advantage of being much more flexible and powerful.

IMO it would be a good idea to read Higher Order Perl and then go back to Design Patterns. I think the insight youll gain from HOP will be very useful in "perlizing" the stuff in design patterns.