In this snapshot we get skulls that can be placed on the ground, wall or you can even wear them as a helmet. Your vision is not obscured wearing these skulls like it is when you wear a pumpkin. In rare instances mobs like zombies, creepers and wither skeletons will drop their skulls as loot. Oh yeah, that wither skeleton. It can be found in the nether wielding a stone sword and when it hits you, you will wither. Your hearts turn black and you lose some (like being poisoned). Once you collect 3 wither skeleton skulls you can make the wither boss that does crazy damage.
Killing a wither boss it will drop a nether star. This is used to create the beacon block. When combined with a pyramid of iron, gold, diamond or emerald blocks it will shoot a light into the sky and gives you a special power while in the radius of the pyramid. They are still working on that.
In a previous snapshot carrots and potatoes were added as a crop to grow and now they will be seen growing in villages. Grab a fishing pole and a carrot, put them together and now you have a carrot on a stick. This will allow you to control the direction of a pig you are riding (also causes other pigs to follow you). I think the controlling pig needs to be tweaked a little bit because right now they will drop off a cliff if you point them in the right direction and they wont jump. Once you’re stuck you can jump of the pig and climb out and it will follow.
Minecraft 1.4 is supposed to be released on or around Halloween and you can download this snapshot here.