You should always create an QApplication instance before trying to use GUI objects/widgets:
Python 2.7.6 (default, Nov 26 2013, 12:52:49)
[GCC 4.8.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from PyQt4 import QtGui
>>> app = QtGui.QApplication([])
>>> obj = QtGui.QGraphicsSimpleTextItem()
>>> obj.setText('foo')
>>>
Its a good idea to add a function to your .pythonrc.py
which does all the necessary imports and setup for a pyqt interactive session - saves a lot of tedious re-typing!