BuddyPress.org

In your code, $user_id doesn’t work because you’re not passing the actual user id.
$user_id->ID would work in this case.

If you’re wondering what the $user variable is in the login_redirect filter, check it out:
http://adambrown.info/p/wp_hooks/hook/login_redirect?version=2.9&file=wp-login.php

Also, have you tried my Pastebin code? It works. I tested it myself.
Just modify what I have there for your own needs.