The way it was supposed to be:
Instead I’m going to show everyone the way it was “supposed” to be. This is not a hack, this Dock was taken from one of the Leopard beta installations that was seeded to developers and beta testers before the official release.
(Via Digg.)
It’s nifty, but I can see why it’s disabled: it hides certain apps (which might be running), and it adds makes everything more complicated.
Moreover, perusing my Dock, I can’t see any app group I’d like to do this to; they’re either important enough I want to have their position fixed, or they’re single apps (like iPhoto) that have no relation to others.