Are there any effective multilevel mob grinders in 1.2.5?

I've seen some of these super high efficiency traps (> 50,000 items/hour) but most of them seem not to work on 1.2.5.

What I was hoping would work would be floors that spawn and let the mobs drop through via pistons (6 blocks that move to the left, pause, then move to the right) but this seems not to work on bukkit.

What you need to do is the following:

• Arrange a large tower of rings that are 1 block wide, separated by 3 blocks vertically:

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• Surround the ring with Pistons facing inward. Place pressure plates on the ring itself, so that stepping on the pressure plate activates the piston and pushes you (or the mob) into the center

• Make sure gaps are filled so that mobs can only spawn directly on the pressure plates.

• Make the stack of rings as high as you can

• Bonus step for exp farms: Work out which height drop will cause mobs to lose all but half a heart of damage. Place creepers within the ring here, and place no spawning rings below this level. This way all mobs will drop the same amount and end up with half a heart and can be easily harvested for exp.

• Plumb in the base of the trap as normal with water/lava to kill mobs and collect items

• ????

• Profit

I've made a small version to test the concept, it seems to work ok. Download my schematic and try it out for yourself.

Here's a very detailed tutorial of making an enderman/exp variant: