public class WebClient

//We create the WebClient with the right encoding and headers:
var webClient = new WebClient();
webClient.Encoding = Encoding.UTF8;
webClient.Headers[HttpRequestHeader.Accept] = "application/xml";

//We submit the request to the server and wait for its response:
string response = await webClient.DownloadStringTaskAsync("http://someAddress.com");

//We modify the response so that it can be deserialized (deserialization is not perfect yet):
response = response.Replace(@"xmlns=""http://NameSpaceOfTheDeserialization""", "");
response = "<ToDoItemsWrapper>" + response.Replace("ArrayOfToDoItem", "ToDoItems") + "</ToDoItemsWrapper>"; // Workaround for the fact that "ArrayOf" types cannot be directly deserialized by the XmlSerializer in this Beta version.

//We create the Deserializer:
var deserializer = new XmlSerializer(typeof(ToDoItemsWrapper));
var memoryStream = new MemoryStream(Encoding.UTF8.GetBytes(response));
var xmlReader = XmlReader.Create(memoryStream);

//We deserialize:
ToDoItemsWrapper items = (ToDoItemsWrapper)deserializer.Deserialize(xmlReader);

// Workaround for the fact that "ArrayOf" types cannot directly be deserialized by the XmlSerializer in this Beta version:
[DataContract]
public class ToDoItemsWrapper
{
    public List<ToDoItem> ToDoItems { get; set; }
}

//We parse the data in a string:
string data = string.Format(@"{{""Id"": ""{0}"",""Description"": ""{1}""}}"Guid.NewGuid(), MyTextBox.Text.Replace("\"", "'"));
//We create the WebClient:
var webClient = new WebClient();
We set the encoding and Headers (note: our data is formatted in json so we set the HttpRequestHeader.ContentType header accordingly) 
webClient.Headers[HttpRequestHeader.ContentType] = "application/json";
webClient.Encoding = Encoding.UTF8;
string response = await webClient.UploadStringTaskAsync("http://cshtml5-rest-sample.azurewebsites.net/api/Todo/", "POST", data);