This morning the Minecraft forums were ablaze as players oggled the new piston mechanics coming in Patch 1.7, also known as the "Adventure Update".  This news relieved a great deal of the tension built up after yesterday's hacker attack that brought down the login servers and the players' spirits.  

Up until now the only way to get these sorts of mechanics was with Piston Mod, but luckily Notch and the gang have seen fit to add the switch-triggered pushing device to the upcoming release.  The video starts off slow, but wait until you get about halfway. Doors, my friend doors.  The mind boggles with the possibilities for sluice gates, door triggers, and so much more.  Can't write more, must start planning how I might use this.