Yep..
I posted on here a few times.. for B v S voice changer.. as well in a Vader thread.
It 'ok'...
I would say before you do ANYTHING research about the volume hack. The stock WaveShield from Adafruit is NOT that loud IMHO at least...
I made a 'customer' version.. where I used all SMD parts.. and merged the Arduino and WaveShield together in one very tiny board. (as the default Arduino Uno and Waveshield take up some serious space! LOL)
pics to compare:
http://dmstudios.net/misc/scab_assembly/all-in-one_2.jpg
http://dmstudios.net/misc/scab_assembly/all-in-one_1.jpg
You can tweak the pitch.. but much more... They have a video of in use on the Adafruit site.. (even has a vader costume on!)