JavaScript Object via JQuery Ajax to an Asp.Net WebMethod

Given the following WebMethod

[WebMethod]
public static string UpdatePerson(Person person)
{
    Person p = Repository.Instance.Get<Person>(person.Guid);
    p.Name = person.Name;
    p.Age = person.Age;
    Repository.Instance.Update(p);

    var result = new WebMethodResult<Person>();
    result.Entity = p;
    return result.ToJson();
}

[DataContract]
public class Person
{
    [DataMember]
    public string Name { get; set; }
    [DataMember]
    public int Age { get; set; }
    [DataMember]
    public string Modified { get; set; }
}

You can call this UpdatePerson method using the following jQuery code snippet.

function updatePerson() {
    var request = {};
    var person = {};
    person.name = "Daffy Duck";
    person.age = 12;
    person.title = "Clown"; //Note that title is not a valid property
    request.person = person;

    var dataString = $.toJSON(request); //using jquery.json
    $.blockUI();

    $.ajax({
        type: "POST",
        url: "Default.aspx/UpdatePerson",
        data: dataString,
        contentType: "application/json; charset=utf-8",
        dataType: "json",
        success: function(json) {
            var data = eval('(' + json.d + ')');
            if (data.hasErrors)
                alert(data.message);
            else {
                alert("updated " + data.entity.Modified);
            }

            $.unblockUI();
        }
    });
}