These screensavers produce absolutely lovely images -- especially the Mandelbrot saver. However, it would be so much more interesting to see the the Mandelbrots growing in process rather than simply the final completed image.
Also, on my system, OS X's System Preferences unexpectedly quit several times while dealing with the more memory intensive of these savers (although, to be honest, it may have been due to a low memory situation created by running multiple apps).