I messed around with crabs a bit earlier, I don't think they trigger pressure plates anymore.
The pressure plates out in the world were all changed to player-triggered-only ones, so if you were using those, it wouldn't work. You need red or green (anything activates those), or yellow (players do not activate, anything else does).
I have a bunny statue set up with pressure plates and bomb statues, and they press the pressure plates properly (you can hear it, and the bombs spawn).
My test setup with bunnies (chiefly to test the design - I hooked it up to bomb statues to mass produce them, although it doesn't take advantage of their rapid cycling):
With wires:
http://puu.sh/4QvVV.pngWithout wires:
http://puu.sh/4QvZI.pngThe switch makes them start spawning, and as they jump on the pressure plates they act like a rapid timer. The high speed button pressing is utterly wasted on bomb statues, obviously, due to the long cooldown they have. (The layout around the platforms, the open space, and the stairs are important to making the bunnies jump onto the platforms and jump around on the pressure plates)
As an aside, when I had it on during a bloodmoon the number of (corrupt) bunnies appeared to grow exponentially, because they were triggering their own statue every time they jumped on one of the pressure plates, and the population limits on the statue were no longer in effect. I assume there was a maximum pop for the area which they eventually hit, or something, since the game never crashed (of course I was killing them too, but they were spawning faster than I could kill them!)
Due to the absurd number of corrupt bunnies spawning in a blood moon in this device, I suspect you could hit an ridiculously high rate of panel pushing (not sure what to test it with).