Noticed results were not returned unless you were logged into the cart.

simple change to catalog/includes/modules/estimated_shipping.asp:

find:
if (tep_session_is_registered('country')) {
if (isset($HTTP_POST_VARS['country'])) {
$country = $HTTP_POST_VARS['country'];


change to:

if (tep_session_is_registered('country')) {
if (isset($HTTP_POST_VARS['country'])) {
$country = $HTTP_POST_VARS['country'];
$estzipcode = $HTTP_POST_VARS['estzipcode'];

More...