OnLamp's Dru Lavigne outlines some clever hacks you can do with FreeBSD and X.org. I believe that the same will work with Linux with X.org. Of particular interests are the following:

Nesting XServers - I did not know you can do it with today's X.org. Pretty cool.

When you install X, you get a whole suite of interesting utilities, many of which you may not be aware of. One of these is Xnest, which allows you to run multiple window managers simultaneously.

Distributed Multihead - it used to be complex to do this in a teaching lab.

One of X's design goals was to work in a networked environment, so there are several cool things you can do if you have access to multiple systems running X. It is remarkably easy for X systems to share display information, so I recommend performing these experiments within a home LAN behind an internet firewall.

So hurry and try them out yourself. :)