For the C# users in this thread, all you need to do is use RestSharp. It will handle the API rather nicely. Here is some sample code to use the WhoAmI method:
var accessToken = "use the documentation to learn how to get this";
var client = new RestClient("http://www.daniweb.com/api");
var request = new RestRequest("me", Method.POST);
request.AddParameter("access_token", accessToken);
var response = client.Execute(request);