Beside a memory leak, there's the possibility of a subtle bug. I had to modify your code slightly, but consider the following class:

use strict;
use warnings;

package Class::SomeMethodMaker;

sub create_accessor {
    my %hash = ();
    return sub {
        my ($self, $value) = @_;
        $hash{$self} = $value if @_ > 1;
        return $hash{$self};
    }
}


package MyClass;


{ no strict 'refs';
  *{"MyClass::colour"} = Class::SomeMethodMaker::create_accessor;
}

sub new {bless {}, shift}

1;

__END__
[download]

It's a simple class with a single accessor.

Now I use this class in the following way:

use strict;
use warnings;
use MyClass;

for my $colour (qw /green yellow/) {
    my $obj = MyClass->new;
    $obj->colour($colour) unless $obj->colour;
    print $obj->colour, "\n";
}

__END__
[download]

You would expect it to print green\nyellow\n. However, it prints green\ngreen\n. The problem is that references are unique - but only references that exist at the same moment in time. References are not necessarely unique over time - they may be reused. Your technique only works if you do some work at DESTROY time - and that makes it trickier.