Reminds me of how holding down shift would cause all of the system animations to go at half speed- this is how Jobs demonstrated the new system animations in OS X 10.0 in September 2000...Another new feature I don't think has been mentioned here yet: there's now an option to mess up the desktop. Right click on the desktop, hold alt and the "clean up" prompt will transform into a literal "mess up" prompt which seems to randomly shuffle the icons all across the desktop.
Might have originally been put in to demonstrate the stacks feature but it's nice that they are keeping it in.