It uses a moving walkway, to kill pretty much any mob that goes into it, and brings the remains to a ladder passageway. To start the device: find all the signs that say "Redstone" go into the hole, and hook up all the redstone (sorry about this but it wouldn't copy, and paste correctly, if it was on). Put what ever you want in the top of it, and enjoy!
My server is fusion.mine.bz
Warp to: meat
Go inside of the butcher house, feel free to destroy (not on server :P) and look at the pistons. and wiring, to build your own!
Also the butcher house will not always be operational, this is due to the lag
This contraption uses a redstone pulsar to power it!

Also do NOT copy and paste this with world edit, it will BREAK pistons!

The story how I came up with this idea was: I was trying to create a moving sidewalk... but it sucked people in and killed them :P so I used "MineCraft" ingenuity :D to come up with a mob killer.

Also this creation CAN lag out a server, if it is not absolutely lag proof!
And if you DO use this on a server, then please give me credit (It took a LONG time)

Oh and feel free to add a redstone clock to replace the pulsar!
Here is a video on how to create the pulsar effect:

Here's a youtube video of me using the butcher house!
Enjoy!