no, it's pretty reliable, since they are all pushed to one location, from which they can't move.Also, thanks for your thread. Everything, from the booster design, to the minecart dispenser design, to the water escalator, and the mobs pressed against the door came from your thread.
dude, just wanna say thanks for spending your time looking through the trash threads for nuggets of goodness so I don't have to. Honestly, I don't even browse the beta-survival section anymore. Anything worth looking at is in your thread.