I am building GNOME with JHBuild using the gnome-3.0 module set. gnome-panel, nautilus and evince are failing to build due to an API change in glib's gio. glib's API change occurred in commit 32f2e9. I raised bugs for each module and linked them to a tracker bug. Is the new GDBusProxy API stable? If yes, API migration is a good way to get started in GNOME development. Not too difficult and appreciated by the developers.
If you too are building and testing GNOME 3.0 there may be some fun ahead!