[Image: http://i1180.photobucket.com/albums/x402/Sarah___/2012-09-10_212952.png]
I've been building the ultimate mob grinder on Tropa's server.
[Image: http://i1180.photobucket.com/albums/x402/Sarah___/2012-09-08_211637.png]
Completely survival, at over 120 blocks tall, uses over 400 repeaters, 800 sticky pistons, 800 pressure plates, and like... 9001 stone. The only mod being used is Better Than Wolves mod, but absolutely no part of this grinder uses the mod(Unless you want to count the automatic stone generator I constructed out of difficult to make materials to help me a bit). It's 100% compatible with vanilla and SMP.
At the moment, I still need upwards of ~550 sticky pistons. All these Ender Pearls are from only three functioning floors, out of a total of 19 spawning floors, meaning that this can get more than 6 times faster than it is right now. From my calculations, you can reach max enchanting level 2 and a half times in five minutes when it's at full efficiency.
At the moment, I'm taking a break to redo my base around the grinder, make it less of an eyesore.
[Image: http://i1180.photobucket.com/albums/x402/Sarah___/2012-09-11_025331.png]