--- switchtheme.module
+++ (clipboard)
@@ -150,7 +150,10 @@
   $form['theme'] = array(
     '#type' => 'select',
     '#default_value' => !empty($custom_theme) ? $custom_theme : $user->theme,
-    '#attributes' => array('title' => t('Change the way this site looks.')),
+    '#attributes' => array(
+      'title' => t('Change the way this site looks.'),
+      'onchange' => 'this.form.submit()',
+    ),
     '#options' => switchtheme_select()
   );
   $form['submit'] = array('#id'=>'switchtheme-submit', '#type' => 'submit', '#value' => t('Switch'));