As Paul mentioned below, much better than mucking with xhost + and tweaking your DISPLAY variable on the remote system, is letting SSH do it for you:
ssh -X firstname.lastname@example.org
which tunnels X11 through an encrypted SSH channel, meaning that
(1) after you SSH, you can run X11 apps without any more setup
(2) your security is much tighter than allowing any X11 from the remote IP to connect to your display
(3) you can work around firewall problems
Really there's no reason to use the method mentioned in the article.