diff -upN rules.orig/rules/modules//node.rules_forms.inc rules/rules/modules//node.rules_forms.inc
--- rules.orig/rules/modules//node.rules_forms.inc	2009-08-25 18:28:58.000000000 +0100
+++ rules/rules/modules//node.rules_forms.inc	2010-03-29 17:56:04.000000000 +0100
@@ -94,6 +94,24 @@ function rules_action_add_node_form($set
   );
 }
 
+/**
+ * Action "Create an automatic node revision log message" configuration form.
+ *
+ */
+function revision_log_action_node_set_log_form($settings = array(), &$form) {
+  $settings += array('log message' => '');
+
+  $form['settings']['log message'] = array(
+    '#type' => 'textarea',
+    '#title' => t('Log message'),
+    '#description' => t('The message to be logged with the new revision.'),
+    '#default_value' => $settings['log message'],
+    '#cols' => 80,
+    '#resizable' => FALSE,
+  );
+}
+
+
 function rules_action_add_node_variable_label($settings) {
   return t('New content of type @type', array('@type' => $settings['type']));
 }
diff -upN rules.orig/rules/modules//node.rules.inc rules/rules/modules//node.rules.inc
--- rules.orig/rules/modules//node.rules.inc	2010-03-26 13:56:01.000000000 +0000
+++ rules/rules/modules//node.rules.inc	2010-03-29 17:27:40.642020207 +0100
@@ -249,6 +249,14 @@ function node_rules_action_info() {
       ),
       'module' => 'Node',
     ),
+    'revision_log_action_node_set_log' => array(
+      'label' => t('Create an automatic node revision log message'),
+      'arguments' => array(
+        'node' => array('type' => 'node', 'label' => t('Content')),
+      ),
+      'module' => 'Node',
+      'eval input' => array('log message'),
+    ),
   );
 }
 
@@ -326,6 +334,22 @@ function rules_action_delete_node($node)
 }
 
 /**
+ * Action "Set a revision log message for the node."
+ *
+ * @param $node
+ * @param $settings
+ *
+ * @return The node to be saved.
+ *
+ */
+function revision_log_action_node_set_log($node, $settings) {
+  // Set the log message.
+  $node->log = $settings['log message'];
+  return array('node' => $node);
+} 
+
+
+/**
  * Implementation of hook_rules_action_info_alter().
  *
  * Adapts the action info of the core actions to better fit for rules.