Update! New version number is 12w07b, fixing the following problems:
Crash bug corrupting levels when spawning mobs above the 255th block
Sheep animation is correct in SMP
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That awkward moment when you find two villagers sexin' on the lawn.
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The End doesn't generate in 12w07a, but the dragon still shows up:
Snapshot 12w07a is out! Higher worlds, Redstone lamps, and more ! (Screenshots)