I can confirm adding "AddressFamily inet" to sshd_config fixed the problem for me after a SSH restart:
$ echo $DISPLAY localhost:10.0 -- X11 forwarding via SSH does not work after upgrade to karmic https://bugs.launchpad.net/bugs/434799 You received this bug notification because you are a member of Ubuntu Server Team, which is subscribed to openssh in ubuntu. -- Ubuntu-server-bugs mailing list Ubuntu-server-bugs@lists.ubuntu.com Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/ubuntu-server-bugs