Well strobe thinks this is an idiot idea, but I really would like to see a VNC Server for quartz. This probably entais finding a way to get at the quartz framebuffer, then porting code. So probably not a terribly interesting project, unless you're totally into VNC.
And here are some ideas for programs that would extend the interface and make it better:
A pipe dream I have would be for someone to reimplement windowshade. You would be a hero for doing this (but Apple may beat you to it in OS X Final -- who knows?)
garlic_b wants a way to have animated desktop pictures a la XEarth -- which would be fun, but not 100% useful.
Having a little background process that monitors for classic symptoms of "hung UI" (like TruBluEnvironment taking 95% of system resources for more than a minute, etc) and then forces a dialog to the front asking if you want to kill the offending process would be cool, though probablly a pain to get completely working. But this would be nice for people who don't have the option to telnet/SSH into their "frozen" boxes to fix things. Or perhaps a background applicaion that waits for a key combination and then forces a super-high-priority terminal window, or process viewer to the front so it is easy to fix things. (Sort of like command-option-escape, but actually useful because you can kill more than just running applications.) But this all relies on being able to forcibly draw things to the screen, which may not be easy.
So if any of these jumps out at you, I think they might be cool additions to the interface.
Zach