Running remote applications on Fedora and Red Hat works out of box, but it doesn't on Ubuntu.
Here is how you can make it work:
Edit the /etc/gdm/gdm.schemas and change:
$ sudo vi /etc/gdm/gdm.schemas
and set it to false
Then restart Xserver or reboot the box and run this command to allow remote hosts to open windows on your Xserver:
$ xhost +