The new de-serializer (JSON.NET) can handle all types of dates. I'm just not sure if the flag for MS AJAX dates needs to be explicitly flipped or whether it's automatically handled. By default ISO dates are auto-parsed for sure.
Output generated from the serializer will always generate dates in ISO format since that's the same format that the native browser serializers use, so this matches the functionality.
Ok, just checked - it works with MS AJAX and ISO dates out of the box and your JSON deserializes just fine.
+++ Rick ---