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.