Index: wp-includes/default-filters.php
===================================================================
--- wp-includes/default-filters.php	(revision 18463)
+++ wp-includes/default-filters.php	(working copy)
@@ -135,6 +135,7 @@
 add_filter( 'the_title', 'convert_chars' );
 add_filter( 'the_title', 'trim'          );
 
+add_filter( 'the_content', 'make_clickable'     );
 add_filter( 'the_content', 'wptexturize'        );
 add_filter( 'the_content', 'convert_smilies'    );
 add_filter( 'the_content', 'convert_chars'      );