Windows Phone FAQ
Windows Phone Best Practices
What should I use for JSON serialization/deserialization?
Third-party libraries such as JSON.net are reported to perform better than .NET's built-in DataContractJsonSerializer, but DataContractJsonSerializer has better type support and uses less memory when passed a ResponseStream of an HttpWebResponse (as opposed to JSON.net's requirement to load the JSON into memory as a string before parsing it). DataContractJsonSerializer is preferred unless performance is tested and shown to be adequate.