Did some more hacking on my Python bindings for Cairo. They are now in the new freedesktop.org CVS server.
I added a cairo.gtk.set_target_drawable() function that sets a Cairo context to draw on an arbitrary GdkDrawable, taking into account the temporary pixmaps used by GTK for its double buffering and the expanded virtual 32-bit coordinate space (based on some of Carl’s code in grrobots).
I ported a few of the Cairo demos to Python/GTK for testing purposes, and they all seem to be working fairly well. The exception is the knockout demo, which doesn’t seem to be redrawing properly (a bad interaction between Cairo and GTK’s double buffering, I guess).