|Think about Loose Coupling|
AFAIK, perl OO consists essentially in 2 (or 3) basic intrinsics and a bunch of usage rules about data structures. So, according to the perl TIMTOWTDI's way of life, you're allowed to do what you want...
Then the following question is: How may I be sure I'm coding what I want?
Practically, the hash data structure is the most genuine to be used as an object (as far as you consider an object as a bag of named properties [aka key/values]).
When you're defining an object, you're implicitly defining a contract which must be followed by everyone whishes derive from your object. This rule defines the interface of your object. Talking about Perl, as object orientation is build as an addon to the language, when devivating you're tied to parent data structure. But talking about objects, heritage is not the only possible relation between objects (quiz: what are the other one?).
Please refer to Perl Design Patterns for more details about perl objects ans the way to associate them.
In reply to Re: Why is a hash the default "object" in oo perl?