David also highlights some other features that didn't make it into his full Leopard review.
Update: Several commenters say Pogue is flat out wrong about this. I don't have Leopard yet so I can't say for sure who is right, but it would be silly of Apple to have removed this feature.
Update 2: It would seem that Pogue was right and I just misread what he wrote. You can drag a hard disk into the Dock, but right clicking on it (or any folder) won't bring up that lovely menu you see to the right. Everything turns into a Stack in the Dock, which is decidedly less helpful if you ask me.