During the last XCode beta, I was playing around with the iPhone simulator and using a proxy I saw the server would respond to geocoding requests with an 'application/x-protobuf' header. That header has since been removed, but the data is still encoded the same (comparing the same request before and after). I was going to try to figure out the RPC encoding method Apple's using, but I lost motivation after reading that they are rate-limiting the API, making it less useful to me.