Here's an idea, should you be looking for one:
How about taking the video from an iSight (or any other connected video device) and streaming it to a .saver, with a few simple FX, like mosaic, echo, QuickTime built-in FX etc.
Perhaps even add a modular structure for other FX plug-ins?
And in the absence of a video stream just some random seeds for the FX?
I'd bet passers by would be tempted to play with it, making it more than just another saver
Shouldn't be too hard?
J