If you haven't run across it already, go take a look at Damian Conway's "Object Oriented Perl". It's a bit dated (the publication date is 2000), but it has a reasonably good exposition on how OO Programming and Design can be implemented in Perl, and what the major pit-falls are. In addition the Ram Book('Perl Cookbook', Christianson & Torkington) has a chapter on Objects, Classes, and Ties that may also be helpful.