Hm... running on OS2007HE, Nokia 770:

~ $ mitter
Traceback (most recent call last):
File "/usr/bin/mitter", line 130, in <module>
main()
File "/usr/bin/mitter", line 123, in main
prefs)
File "/usr/lib/python2.5/site-packages/mitterlib/ui/ui_pygtk.py", line 88, in __init__
self.add_grid()
File "/usr/lib/python2.5/site-packages/mitterlib/ui/ui_pygtk.py", line 298, in add_grid
self.message_renderer.set_property('wrap-mode', gtk.WRAP_WORD)
TypeError: object of type `GtkCellRendererText' does not have property `wrap-mode'

pygtk version:
ii python2.5-gtk2 2.10.3-1osso9 Python bindings for the GTK+ widget set

tty is fine, though.