I'm so happy to see Json.NET being baked into Web API, however, I still have to write my own custom MediaTypeFormatter to support Bson. Json.NET supports this very easily using the same JsonSerializer.
Bson uses the same JsonSerializer / JsonSerializerSettings. BsonReader and BsonWriter inherit from JsonReader, JsonWriter respectively.
Please consider adding support for this. Thanks!
See discussion: http://aspnetwebstack.codeplex.com/discussions/359698