Notch is a genius!
Look at that hidden door. :O
Also, slime balls have a use, finally.
Edit: Wait, he didn't show what happens when you place a piston on a (sticky) piston. You could easily create elevators if it would work the way I think it would.
Edit 2: Omg, we can now fit the pyramid with actual traps. D:
Edit 3: Omg omg, if we had a block that destroys other blocks and one that can place other blocks we could create automated treefarms.
Edit 4: Omg omg omg I need to breathe.
Edit 5: Omg omg omg omg he DID show it. You can stack pistons on top of each other. WE CAN BUILD ELEVATORS NOW!