PadmaColors is a Japanese weblog that has figured out how to 'hack' DashSaver, my Dashboard as a screensaver app, to change the default background.
This is awesome. I'm impressed when people using hacking in such a good way. Of course, it may have been easier to ask me, since I am adding this feature in the next version. But I'm sure asking isn't nearly as much fun. :)
I'll make sure and let me them know when I release the next version. I imagine changing the preferences is a little easier then hex editing. What's also interesting is how much you can find out about how a program was written (function calls, data, etc.) from the hexEditor.
DashSaver is also mentioned on WoodenShips.