On my Mac Pro, I have my normal account and a guest account setup for friends who come in my room that may want to use my computer. My screen saver is set up to automatically come on after ten minutes, and it is password protected, but if somebody wants to use my computer they can click "Switch User" as I have fast user switching enabled. Anyway when they click this, the screen goes all crazy for a moment as the Quartz Extreme cube action happens, then it goes back to normal. This does this with every screen saver I have tried. Is there a reason it does this? Does it do this for anybody else?