(And while reading that and thinking "I swear I recently read something else talking about applying TCP congestion control to RPC queueing". And indeed I had: http://www.evanjones.ca/prevent-server-overload.html)
Had a co-worker implement something similar to this dynamic throttling in a back-end analytical process, based around access of a DynamoDB table that was accessed by multiple front end services.
The code on the back-end processing software would throttle itself back hard (about 50% of the speed it had reached) whenever it ran into a DynamoDB throttle message as a response, and then would ramp itself back up steadily. Combined with good retry logic on the front end services, it meant we could keep the DynamoDB table humming along at near maximum usage.
I did this almost 10 years ago for accessing Amazon SimpleDB, too: http://www.daemonology.net/blog/2008-06-29-high-performance-...