So the embarking track auto picks up mobs? Or does it need a pulse? Either way what is the range of the embarking track? And how would you suggest the slaughter house be made? Thanks

. Any more suggesting keep them coming thanks

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If I'm not mistaken, the embarking track will automatically suck a nearby mob (or player) into any cart passing over it. It may need a constant redstone signal, but I don't think it needs to be pulsed.
Also note that control tracks are recommended whenever a cart must pass through an enclosure that contains mobs, as a cart won't be pushed backwards by cows that will certainly show up in the way. I have also heard that animals in minecarts can still breed, but won't be picked up by embarking tracks.
As for the slaughterhouse... You could try a drop trap, a vanilla-style "thin blade of lava" (perhaps using cover strips or corners to hold the lava in place, instead of ladders/signs), cacti, Xycraft Crystals (the little tiny crystal-shaped "quartz crystals" that spawn underground in the Overworld), melee turtles, brainy Thaumcraft Iron Golems, Redpower Igniters, or MFR's Grinder that I mentioned in my post above.
The advandage to turtles or golems (with visors as well as the Intelligence Core) is that you get to keep the XP. The grinder will do kind of the same thing, but it instead produces liquid "Mob Essence", as I explained above, which can be used for enchanting.
As a final note, if you're using Railcraft to transport mobs, I will recommend the Disposal Track. It's a combination of the Suspended and Disembarking tracks- it does not need a block directly under it (Floating bridges!), and will cause minecarts to dump any mob or player riding them. And did I mention that the tracks aren't solid (except to minecarts), either?