Ugh. Not 100% sure it's related, but I've been getting a similar traceback when running pip's test suite (python setup.py test) on OSX 10.6.8 with Python 2.7.2.

Traceback (most recent call last):
  File "/usr/local/Cellar/python/2.7.2/Frameworks/Python.framework/Versions/2.7/lib/python2.7/atexit.py", line 24, in _run_exitfuncs
    func(*targs, **kargs)
  File "/usr/local/Cellar/python/2.7.2/Frameworks/Python.framework/Versions/2.7/lib/python2.7/multiprocessing/util.py", line 284, in _exit_function
    info('process shutting down')
TypeError: 'NoneType' object is not callable

Obviously it's not the exact same bug as fixed here, but Googling the traceback led me here and I do think it's the same genre of bug, i.e., multiprocessing's use of forking leads to issues when atexit is called (wasn't sure whether to open it here or #9207). Also, see https://groups.google.com/forum/#!topic/nose-users/fnJ-kAUbYHQ, it seems other users of the nose testsuite ran into this.

I'm afraid I won't have time to look much further into this (the reason I'm running pip's testsuite is that I'm already trying to make a contribution to pip...), but I thought it's best to at least mention it somewhere.