Multiple reviews by same person.

Ok, here is the hack to allows users to make multiple reviews.

To get the needed variable into the admin GUI so this feature can be turned on or off at will...

below this code (which ends at line 237 of the userreview.module)
$form['current review']['userreview_show_currentuser_review'] = array(
'#type' => 'checkbox',
'#title' => t('Show current user\'s review'),
'#description' => t('When showing a reviewed node (in full page view), should current\'s user review be shown?'),
'#default_value' => variable_get('userreview_show_currentuser_review', true)
);

add these lines:
$form['current review']['userreview_allow_multiple_reviews'] = array(
'#type' => 'checkbox',
'#title' => t('Allow multiple reviews of one node.'),
'#description' => t('Should a user be allowed to make more than one review per node? (disables "Show current user\'s review")'),
'#default_value' => variable_get('userreview_allow_multiple_reviews', false)
);

-----------------
Then (to actually allow multiple reviews)
in the fuction:
function userreview_nodeapi(&$node, $op, $teaser = NULL, $page = NULL) {

replace:
//get the current user's review for this content node
$userreviewnode = get_userreview_node($node, $user->uid);

with:
//get the current user's review for this content node
if (variable_get('userreview_allow_multiple_reviews', false)) {
$userrewviewnode = null;
} else {
$userreviewnode = get_userreview_node($node, $user->uid);
}