Similarly to bug 623965 (pygtk), pygobject uses the PyCObject API to pass around API hooks:
  http://git.gnome.org/browse/pygobject/tree/gobject/pygobject.h

This API is deprecated in Python 2.7; see:
  http://docs.python.org/dev/whatsnew/2.7.html#capsules

This leads to gobject._gobject failing to be imported if the default warning settings (ignore deprecation warnings) are overridden:

Overriding to an error leads to a hard failure of the python process:
Python 2.7 (r27:82500, Jul 28 2010, 18:07:57) 
[GCC 4.5.0 20100716 (Red Hat 4.5.0-3)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import warnings
>>> print warnings.filters
[('ignore', None, <type 'exceptions.DeprecationWarning'>, None, 0), ('ignore', None, <type 'exceptions.PendingDeprecationWarning'>, None, 0), ('ignore', None, <type 'exceptions.ImportWarning'>, None, 0), ('ignore', None, <type 'exceptions.BytesWarning'>, None, 0)]
>>> warnings.filterwarnings('error')
>>> import gobject
python: /root/rpmbuild/BUILD/Python-2.7/Objects/dictobject.c:759: PyDict_SetItem: Assertion `value' failed.
Aborted

Clearing the filters leads to just a warning:

Python 2.7 (r27:82500, Jul 28 2010, 18:07:57) 
[GCC 4.5.0 20100716 (Red Hat 4.5.0-3)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import warnings
>>> warnings.filters=[]
>>> import gobject
/usr/lib64/python2.7/site-packages/gtk-2.0/glib/__init__.py:22: PendingDeprecationWarning: The CObject type is marked Pending Deprecation in Python 2.7.  Please use capsule objects instead.
  from glib._glib import *
/usr/lib64/python2.7/site-packages/gtk-2.0/gobject/constants.py:24: PendingDeprecationWarning: The CObject type is marked Pending Deprecation in Python 2.7.  Please use capsule objects instead.
  import gobject._gobject