A developer by the name of [ghostwalker] has managed to not only get X11 running on Android, but has also assembled a how-to guide
should you feel inclined to try this type of thing for yourself. The
end product of this little experiment results in you being able to
literally run a fully fledged Linux desktop environment on your G1.
However, there are a few little hang-ups which you will need to
overcome if you are to be successful with this endeavor.
The X Window System, also known as X or X11, is a computer software
system and network protocol that provides a GUI for networked
computers. In order to get this running on your Android device, you
need to already have a Debian shell on the phone. You will also need a copy of Andoird VNC viewer or a similar VNC client in order to avoid needing a custom display driver.
Although slightly technical and clearly for the linux enthusiasts,
it is still kinda cool. If you want to know more head on over here to find out all the relevant information.