gistfile1.php

<?php

add_filter("gform_pre_render", "populate_dropdown");
function populate_dropdown($form){
    global $current_user;
    get_currentuserinfo();
    
    foreach($form['fields'] as &$field) {
        if($field['inputName'] == 'email') {
        
            $email = xprofile_get_field_data('email', $current_user->ID);
            $field['choices'] = array(
                array('text' => $email, 'value' => $email, 'isSelected' => ''),
                array('text' => $email, 'value' => $email, 'isSelected' => ''),
                array('text' => $email, 'value' => $email, 'isSelected' => '')
                );
            
        }
    }
    
    return $form;
}

?>