Minecraft wiki entry for Development_versions, associated text: Crafted from 4 honey bottles.
The bottles are not consumed and will remain in the crafting grid.
Walking is slowed, and jump height is reduced.
Effect also works through non-full blocks like carpet, trapdoors and slabs.
If an entity is on a honey block that is pushed by a piston, the entity will be moved with the honey block.
Entities touching the side of a honey block slide down slowly.
Landing on a honey block reduces fall damage.
Fall damage is cut to about 1⁄5 of normal: equal to ceiling(fall distance - 3) / 5), or in other words, 1⁄5 of 1 for every block fallen after the first 3, rounded up.
When a honey block is pushed or pulled by a piston, it attempts to move all adjacent blocks in the same direction.
Works the same way as slime blocks.
Mobs will usually avoid walking on them.
Does not conduct redstone signals.
Bees will occasionally 'eat' from them if placed near beehives or bee nests.