Index: wp-includes/ms-default-filters.php
===================================================================
--- wp-includes/ms-default-filters.php	(revision 17283)
+++ wp-includes/ms-default-filters.php	(working copy)
@@ -17,7 +17,6 @@
 add_filter( 'wpmu_validate_user_signup', 'signup_nonce_check' );
 add_action( 'init', 'maybe_add_existing_user_to_blog' );
 add_action( 'wpmu_new_user', 'newuser_notify_siteadmin' );
-add_action( 'wpmu_activate_user', 'add_new_user_to_blog', 10, 3 );
 add_action( 'sanitize_user', 'strtolower' );
 
 // Blogs