Reitter: Answering the question: "How do I develop an app for GNOME?"

This whole thread is indicative of a real problem and I would look to the kernel for guidance. The kernel deprecates APIs but maintains and ships the old ABI, usually by having it be a shim layer to the new API. If GNOME 3 were to do the same thing then they would ship all of the GNOME 2 libraries or at least compatible stubs and consider them all part of the ABI, indefinitely. They wouldn't rely on the downstream distributors to individually package the pieces and parts and would make it easy for them to maintain ABI compatibility.

That's not the world we live in though, user space, long term compatibility isn't the biggest priority.