As you know, 1.2 came out, and to some of you it's a problem.
Mobs are now smart enough to not fall in pits or get trapped from a wall, and that is REALLY NOT helpful for making mob traps.
So now your trap won't work, so FORCE them to fall into something... By using water currents!
Mobs cannot outrun water currents like you can.
This can be helpful for making Fall Traps, Grind Traps, or even Drown Traps!
I hope this helps with your traps!