We use it. It's pretty good. It has a lot of places you can hook in extra functionality. You get most of the HTTP error status codes for free, but we also have

We use it. It's pretty good. It has a lot of places you can hook in extra functionality. You get most of the HTTP error status codes for free, but we also have a filter that looks at outgoing protobuf messages for a certain field that indicates the messages is a response to a create request, and that allows us to return an HTTP 202 instead of 200. We were even able to do Amazon-style request signing. One thing about request signing is that if you use protobuf key-value maps, the order is not deterministic on the wire. This broke our signing. Key-value maps are kind of a protobuf hack anyway, so we ended up using an array of structs. When it came time to add the JSON gateway, we found it pretty easy to write custom JSON serialization/deserialization code to convert the structs to a JSON map. This is all in Go by the way.