So I've used this setup before on just a plain piezo on the table:http://leucos.lstilde.org/wp/2009/06/piezo-transducer-signal-conditioning/
It worked great for just controlling a solenoid (what I was using it for).
I'm now building some drum triggers into my acoustic drums to drive an Arduino which will send MIDI data.
I've seen most drum triggers use a foam cone similar to this:http://www.electricdrumcenter.com/4-foam-cones-trigger-for-diy-electronic-drum/
I plan on incorporating some threshold control into the circuit (with a pot), but I want the triggers to be as sensitive as possible. The circuit above seems to clean/condition the signal a bunch, but that's just a raw piezo being used (as are most other arduino triggers I've seen on here).
I guess it's more about if anyone has used one of those foam cones in a trigger circuit.