py3k branch gives another error now, when running test_multiprocessing 
in a tight loop:

test test_multiprocessing failed -- Traceback (most recent call last):
  File "/Users/cartman/Sources/py3k/Lib/test/test_multiprocessing.py", 
line 1163, in test_remote
    queue = manager2.get_queue()
  File "/Users/cartman/Sources/py3k/Lib/multiprocessing/managers.py", 
line 641, in temp
    authkey=self._authkey, exposed=exp
  File "/Users/cartman/Sources/py3k/Lib/multiprocessing/managers.py", 
line 893, in AutoProxy
    incref=incref)
  File "/Users/cartman/Sources/py3k/Lib/multiprocessing/managers.py", 
line 702, in __init__
    self._incref()
  File "/Users/cartman/Sources/py3k/Lib/multiprocessing/managers.py", 
line 749, in _incref
    dispatch(conn, None, 'incref', (self._id,))
  File "/Users/cartman/Sources/py3k/Lib/multiprocessing/managers.py", 
line 85, in dispatch
    raise convert_to_error(kind, result)
multiprocessing.managers.RemoteError: 
------------------------------------------------------------------------
---
Traceback (most recent call last):
  File "/Users/cartman/Sources/py3k/Lib/multiprocessing/managers.py", 
line 187, in handle_request
    result = func(c, *args, **kwds)
  File "/Users/cartman/Sources/py3k/Lib/multiprocessing/managers.py", 
line 403, in incref
    self.id_to_refcount[ident] += 1
KeyError: '7389d0'