Minecraft wiki entry for Development_versions, associated text: Is now controllable by redstone – Power it to disable item forwarding.
Added a proper icon.
Is no longer considered wooden (cannot be used as a fuel in a furnace, etc.).
New crafting recipe uses iron ingots rather than stone.
The redstone signal emitted when a redstone comparator is placed against it directly has changed.
1 item will give a signal strength of 1, a 1/3 of a stack (21 for items which stack to 64) gives a signal strength of 2.
The number of full stacks x 3 = Signal strength.
E.g. 2 stacks of an item/block will give a signal strength of 6, while 2 potions will also give a signal strength of 6 (because a potion occupies one stack).