Elevators. Airlocks for an underwater city. Traps. Stone generators. Auto-fill mechanisms for bays (again, for said underwater city). Redstone circuitry. Drop-down lighting. A switching house for rail cars.
That's just off the top of my head... there are tons of possibilities!
Nothing. I didn't found any slimes yet, and they are removing the duplication glitch in the bugfix update so I expect to have a very limited amount of sticky pistons until 1.8 and creative mode comes out.
3x3 hidden door behind a hidden waterfall entrance that leads to my seemingly plain square room that opens to show multiple areas of the house. its gonna be sweet.....
what will YOU do?
That's just off the top of my head... there are tons of possibilities!
I love pistons. One of best additions imo.
Plus cactus traps, mob crushers, retractable bridges, and the works.
Also, secret doors into hidden rooms, mines and whatnot. Can't wait for pistons.