These all seem immediately practical status codes that add semantics I've been wanting. Great! In particular I am happy about the 429 Too Many Requests header, as every time I've done rate throttling I've had to quibble over what code to actually send back.
What code did you use? I've typically used a 408 in a throttling use case but it never seemed to fit well (our client handled this response from our server with an exponential back off so we were not relying on another client to handle it correctly).
503 seems the most appropriate of the current codes ("The server is currently unable to handle the request due to a temporary overloading or maintenance of the server. The implication is that this is a temporary condition which will be alleviated after some delay.")
