Directly from perlbot:

An inheritable constructor should use the second form of bless() which allows blessing directly into a specified class. Notice in this example that the object will be a BAR not a FOO, even though the constructor is in class FOO.

package FOO;

sub new {
    my $type = shift;
    my $self = {};
    bless $self, $type;
}

sub baz {
    print "in FOO::baz()\n";
}

package BAR;
@ISA = qw(FOO);

sub baz {
    print "in BAR::baz()\n";
}

package main;

$a = BAR->new;
$a->baz;
[download]

There is IMO nothing to add :) Re-using constructors is generally a good idea, as it makes the code more maintainable.