The latest snapshot has been released, 12w08a. The most exciting addition is the Iron Golems! They are spawned near villages that have a population of at least 15 to protect them from the Zombie invasions. (for information on the Zombie invasions, then visit this article) They are large robotic looking creatures, that share the Squidward features with the Villagers. Their health is 100 (50 hearts) and their attack is 7 – 20, (3 and half hearts – 10 hearts) the potential to one hit kill its victim. They get damage from lava, fire and by drowning, but to not take any damage from falling. Golems carry Roses, and give them to villager children, symbolising the friendly relationship between the two mobs.
Once one has been killed, it can drop from 3-5 Iron Ingots and up to 2 roses.
Alongside the introduction of the Iron Golem, upside down stairs have been added. I can only think that this addition is purely for decorative purposes, as upside down stairs wont be very useful with the presence of gravity.
The camera control for filming has been improved with many more ways to change camera angle, and fix into a position.
For more information on the snapshot, then please visit the Minecraft Wiki.