Thanks to a link on 2lmc spool, I installed the truly wonderful Electric Sheep screensaver. In fact, it's a rather superior species of screen saver, in which your own computer becomes part of a huge network of interconnected machines collaboratively creating and rendering lovely fractal-like, abstract, moving images, which constantly shift and morph into one another. These images are called sheep. What's more, if you like one of the images you see you can vote for it by pressing the up arrow. The votes are then used as part of a weighting process in a genetic algorithm to breed more sheep. Popular sheep live longer (and presumably reproduce more), and so the sheep evolve into ever more beautiful forms.