Index: misc/drupal.js
===================================================================
RCS file: /cvs/drupal/drupal/misc/drupal.js,v
retrieving revision 1.58
diff -u -p -r1.58 drupal.js
--- misc/drupal.js	31 Aug 2009 05:51:07 -0000	1.58
+++ misc/drupal.js	10 Oct 2009 19:36:15 -0000
@@ -109,6 +109,21 @@ Drupal.checkPlain = function (str) {
 };
 
 /**
+ * Prefill form fields with information from the visitor cookie informaiton.
+ */
+Drupal.addVisitorCookieInfo = function (form_id) {
+  $('form#' + form_id).once('addVisitorCookieInfo', function () {
+    $.each(['name', 'mail', 'homepage'], function () {
+      var element = $('form#' + form_id + ' [name=' + this + ']');
+      var cookie = $.cookie('Drupal.visitor.' + this);
+      if (element.length && cookie) {
+        element.val(cookie);
+      }
+    });
+  });
+}
+
+/**
  * Translate strings to the page language or a given language.
  *
  * See the documentation of the server-side t() function for further details.
Index: modules/comment/comment.js
===================================================================
RCS file: /cvs/drupal/drupal/modules/comment/comment.js,v
retrieving revision 1.13
diff -u -p -r1.13 comment.js
--- modules/comment/comment.js	9 Oct 2009 15:39:12 -0000	1.13
+++ modules/comment/comment.js	10 Oct 2009 19:36:16 -0000
@@ -3,12 +3,7 @@
 
 Drupal.behaviors.comment = {
   attach: function (context, settings) {
-    $.each(['name', 'homepage', 'mail'], function () {
-      var cookie = $.cookie('Drupal.visitor.' + this);
-      if (cookie) {
-        $('#comment-form input[name=' + this + ']', context).once('comment').val(cookie);
-      }
-    });
+    Drupal.addVisitorCookieInfo('comment-form');
   }
 };
 
Index: modules/contact/contact.js
===================================================================
RCS file: /cvs/drupal/drupal/modules/contact/contact.js,v
retrieving revision 1.1
diff -u -p -r1.1 contact.js
--- modules/contact/contact.js	9 Oct 2009 15:39:12 -0000	1.1
+++ modules/contact/contact.js	10 Oct 2009 19:36:16 -0000
@@ -2,13 +2,8 @@
 (function ($) {
 
 Drupal.behaviors.contact = {
-  attach: function(context) {
-    $.each(['name', 'mail'], function () {
-      var cookie = $.cookie('Drupal.user.' + this);
-      if (cookie) {
-        $('#contact-site-form input[name=' + this + ']', context).once('comment').val(cookie);
-      }
-    });
+  attach: function (context, settings) {
+    Drupal.addVisitorCookieInfo('contact-site-form');
   }
 };
 
Index: modules/user/user.js
===================================================================
RCS file: /cvs/drupal/drupal/modules/user/user.js,v
retrieving revision 1.18
diff -u -p -r1.18 user.js
--- modules/user/user.js	21 Sep 2009 08:52:41 -0000	1.18
+++ modules/user/user.js	10 Oct 2009 19:36:16 -0000
@@ -188,4 +188,10 @@ Drupal.behaviors.userSettings = {
   }
 };
 
+Drupal.behaviors.userRegistration = {
+  attach: function (context, settings) {
+    Drupal.addVisitorCookieInfo('user-register');
+  }
+};
+
 })(jQuery);
Index: modules/user/user.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/user/user.module,v
retrieving revision 1.1060
diff -u -p -r1.1060 user.module
--- modules/user/user.module	10 Oct 2009 16:48:39 -0000	1.1060
+++ modules/user/user.module	10 Oct 2009 19:36:17 -0000
@@ -3080,6 +3080,9 @@ function user_register_form($form, &$for
     $form['account']['#type'] = 'markup';
   }
 
+  $form['#attached']['library'][] = array('system', 'cookie');
+  $form['#attached']['js'][] = drupal_get_path('module', 'user') . '/user.js';
+
   $form['submit'] = array(
     '#type' => 'submit',
     '#value' => t('Create new account'),