Personally, I really like Design Patterns, but you always have to take them with a grain of salt, much more like a metaphor or legend than a design specification, describing in an abstract way, how a certain class of problems has been approached and what the consequences of that approach were. They also allow me to communicate easier with other people, as a Design Pattern creates a common name for something that would have to be described otherwise.
When looking at Design Patterns, you must decide, if you are the intended audience. The GoF book focuses on a C++ audience - Perl already has other idioms that deal with many of the patterns, for example the Iterator pattern, which is simply foreach, so not all patterns you find in the GoF book are directly useful for a Perl programmer (and in fact, not many are useful with a dynamic language).
But patterns are also available for user interface design and other stuff, and these patterns can be helpful, if you want to provide a feature, but don't know yet, how it could be presented to the user.
perl -MHTTP::Daemon -MHTTP::Response -MLWP::Simple -e ' ; # The
$d = new HTTP::Daemon and fork and getprint $d->url and exit;#spider
($c = $d->accept())->get_request(); $c->send_response( new #in the
HTTP::Response(200,$_,$_,qq(Just another Perl hacker\n))); ' # web
