The reason I want to do this is because users develop against our API with JavaScript, and some developers screw up and cause visitors to slam the server with AJAX requests. When this happens, I want to be able to throttle the API requests to perhaps 50 requests per minute, or something to that effect.
Note: (particularly DB intensive resources, so perhaps at a path level, rather than server-wide (e.g. throttle "/json_api/", but not "/static/").