Hmm, I'm hard-pressed to argue that point. If I were to come up with something else, I would argue that the lack of multi-method dispatch is a pretty big problem. Of course, that's sort of cheating because if you get that, it automatically implies proper argument handling and I therefore get two for the price of one :)

Unfortunately, I've seen those who have not had a chance to work extensively with MMD aren't terribly impressed by its benefits. My suggestion to them would be to take a program written in a language which supports this and try to port it to Perl. It leads to monstrosities like the constructor for AI::Prolog::Term:

sub new {
    my $proto = shift;
    my $class = CORE::ref $proto || $proto; # yes, I know what I'm doi
+ng
    return $class->_new_var unless @_;
    if (2 == @_) { # more common (performance)
        return _new_from_functor_and_arity($class, @_) unless 'ARRAY' 
+eq CORE::ref $_[1];
    }
    elsif (1 == @_) {
        my $arg = shift;
        return _new_with_id($class, $arg)     if ! CORE::ref $arg && $
+arg =~ /^[[:digit:]]+$/;
        return _new_from_string($class, $arg) if ! CORE::ref $arg;
        return $arg->_term($class)            if   CORE::ref $arg && $
+arg->isa(Parser);
    }
    require Carp;
    Carp::croak("Unknown arguments to Term->new");
}
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That constructor was buggy for a long time because Perl doesn't support MMD. It was very frustrating.