Look like I isolated the problem. It seems multiprocessing is using cPickle which cannot be extended with ForkingPickler, unlike the Python version of the pickle module.

15:09:29 [ ~/pythondev/python2.7 ]$ ./python.exe issue10717.py
Traceback (most recent call last):
  File "issue10717.py", line 8, in <module>
    p.apply(Test().hello, ("jimbo",))
  File "/Users/avassalotti/PythonDev/python2.7/Lib/multiprocessing/pool.py", line 244, in apply
    return self.apply_async(func, args, kwds).get()
  File "/Users/avassalotti/PythonDev/python2.7/Lib/multiprocessing/pool.py", line 558, in get
    raise self._value
cPickle.PicklingError: Can't pickle <type 'instancemethod'>: attribute lookup __builtin__.instancemethod failed