When using Zend_Form_Element_Checkbox elements, getValue returns either 1 (checked) or 0 (unchecked). I find that great. However, the current setValue works differently:

public function setValue($value)
{
    $value = ($value === null) ? 0 : 1;
    $this->checked = ($value === 0) ? false : true;
    return parent::setValue($value);
}

Anything other than null, sets the checkbox value to 1 (even 0 or '0'). I would suggest keeping it consistent with getValue, something along these lines:

public function setValue($value)
{
    if ($value === null) $value = 0;
    $this->checked = ($value == 0) ? false : true;
    return parent::setValue($value);
}

I would also suggest allowing the value to be a string ('0' or '1') -> thus a ==. This will allow populating with the data straight from the DB.