Hi ! Here is Mac Mountain Lion + Pd-extended last version, Macbook Pro 2011, 8Gb.
I have connected my MIDI M-audio KeyStudio 49 keyboard, ok. Testing MIDI and a small patch with [notein] shows that Pd receives the notes.
I connected [notein] to [mtof] to [dac~] but impossible to get any sound ! I tried every configuration. The last is :
AUDIO : IN1 = (0)Built-in Input, OUT1 = (0)built-in Output, latency = 20
MIDI : IN1 = Key-Studio, OUT1 = none
Portaudio (tried with Jack, no success)
PLEASE 
Otherwise no problems, without MIDI sound is ok.
Thanks,
-wissme-