Now just for PGP support.
You don't want server side PGP support - you'd have to give your private key to Google. As much as I trust Google, I still don't trust them that much.
Much more secure to handle the crypto client side. Ideally, Google should work with the firegpg guy so that he has notice before they change the interface (FireGPG tends to break for a day or two whenever there is any change to the GMail UI).
You would probably have to not use Google, since if they are unable to read your email, that kind of destroys their business model.