Index: captcha.install
===================================================================
--- captcha.install	(revision 30487)
+++ captcha.install	(working copy)
@@ -114,6 +114,13 @@
   // what to do after install?
   drupal_set_message($t('You can now <a href="!captcha_admin">configure the CAPTCHA module</a> for your site.',
     array('!captcha_admin' => url('admin/user/captcha'))), 'status');
+
+  // explain to users that page caching may be disabled
+  if (variable_get('cache', 0) > 0) {
+    drupal_set_message($t('Note that the CAPTCHA module disables <a href="!performance_admin">page caching</a> on pages that include a CAPTCHA challenge.',
+      array('!performance_admin' => url('admin/settings/performance'))), 'status');
+  }
+
 }
 
 /**