Add Current users WPMU to All Future Blogs Created by Admin
<?php
add_action('wpmu_new_user', 'reg_user_as_contributor');
function reg_user_as_contributor($user_id){
$blog_array = get_blogs_of_user(1);
foreach($blog_array as $admin_blog){
add_user_to_blog( $admin_blog->userblog_id, $user_id, 'contributor' );
}
}
?>