has a neat guide to the new iTunes visualizer:

M - Changes the mode, cycling through what it has to offer
N - Toggles 'Nebula Mode' which adds colored clouds to the mix...maybe they're processor hogs and need to be removed on slower systems?
L - Toggles the camera lock that keep the point of view grooving to the tunes

More on Merc. I haven't seen that N does much yet, but maybe I'm losing it.