The documentation and examples available at pygtk.org weren't bad, when I first dipped my toes into Gtk+ programming in Python a few years ago.
Now, with the switch to PyGObject-Introspection, things are a bit more cloudy. There is a nice Gtk+ 3 in Python tutorial out there, built with Sphinx (the documentation tool, not the search index), but I don't remember the URL.
I've received a patch to convert my PyGtk project to PyGI (I don't think I could've managed to do that myself), and I manage to maintain it, barely, by referring to the C API documentation and translating it into Python syntax. Also, people on IRC are helpful (#pygtk on irc.gnome.org).